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diff --git a/doc/src/sgml/html/plpgsql-control-structures.html b/doc/src/sgml/html/plpgsql-control-structures.html new file mode 100644 index 0000000..e1133b7 --- /dev/null +++ b/doc/src/sgml/html/plpgsql-control-structures.html @@ -0,0 +1,943 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>43.6. Control Structures</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="plpgsql-statements.html" title="43.5. Basic Statements" /><link rel="next" href="plpgsql-cursors.html" title="43.7. Cursors" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">43.6. Control Structures</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpgsql-statements.html" title="43.5. Basic Statements">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpgsql.html" title="Chapter 43. PL/pgSQL — SQL Procedural Language">Up</a></td><th width="60%" align="center">Chapter 43. <span class="application">PL/pgSQL</span> — <acronym class="acronym">SQL</acronym> Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpgsql-cursors.html" title="43.7. Cursors">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLPGSQL-CONTROL-STRUCTURES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">43.6. Control Structures</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING">43.6.1. Returning from a Function</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING-PROCEDURE">43.6.2. Returning from a Procedure</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-CALLING-PROCEDURE">43.6.3. Calling a Procedure</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CONDITIONALS">43.6.4. Conditionals</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CONTROL-STRUCTURES-LOOPS">43.6.5. Simple Loops</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING">43.6.6. Looping through Query Results</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-FOREACH-ARRAY">43.6.7. Looping through Arrays</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-ERROR-TRAPPING">43.6.8. Trapping Errors</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CALL-STACK">43.6.9. Obtaining Execution Location Information</a></span></dt></dl></div><p> + Control structures are probably the most useful (and + important) part of <span class="application">PL/pgSQL</span>. With + <span class="application">PL/pgSQL</span>'s control structures, + you can manipulate <span class="productname">PostgreSQL</span> data in a very + flexible and powerful way. + </p><div class="sect2" id="PLPGSQL-STATEMENTS-RETURNING"><div class="titlepage"><div><div><h3 class="title">43.6.1. Returning from a Function</h3></div></div></div><p> + There are two commands available that allow you to return data + from a function: <code class="command">RETURN</code> and <code class="command">RETURN + NEXT</code>. + </p><div class="sect3" id="id-1.8.8.8.3.3"><div class="titlepage"><div><div><h4 class="title">43.6.1.1. <code class="command">RETURN</code></h4></div></div></div><pre class="synopsis"> +RETURN <em class="replaceable"><code>expression</code></em>; +</pre><p> + <code class="command">RETURN</code> with an expression terminates the + function and returns the value of + <em class="replaceable"><code>expression</code></em> to the caller. This form + is used for <span class="application">PL/pgSQL</span> functions that do + not return a set. + </p><p> + In a function that returns a scalar type, the expression's result will + automatically be cast into the function's return type as described for + assignments. But to return a composite (row) value, you must write an + expression delivering exactly the requested column set. This may + require use of explicit casting. + </p><p> + If you declared the function with output parameters, write just + <code class="command">RETURN</code> with no expression. The current values + of the output parameter variables will be returned. + </p><p> + If you declared the function to return <code class="type">void</code>, a + <code class="command">RETURN</code> statement can be used to exit the function + early; but do not write an expression following + <code class="command">RETURN</code>. + </p><p> + The return value of a function cannot be left undefined. If + control reaches the end of the top-level block of the function + without hitting a <code class="command">RETURN</code> statement, a run-time + error will occur. This restriction does not apply to functions + with output parameters and functions returning <code class="type">void</code>, + however. In those cases a <code class="command">RETURN</code> statement is + automatically executed if the top-level block finishes. + </p><p> + Some examples: + +</p><pre class="programlisting"> +-- functions returning a scalar type +RETURN 1 + 2; +RETURN scalar_var; + +-- functions returning a composite type +RETURN composite_type_var; +RETURN (1, 2, 'three'::text); -- must cast columns to correct types +</pre><p> + </p></div><div class="sect3" id="id-1.8.8.8.3.4"><div class="titlepage"><div><div><h4 class="title">43.6.1.2. <code class="command">RETURN NEXT</code> and <code class="command">RETURN QUERY</code></h4></div></div></div><a id="id-1.8.8.8.3.4.2" class="indexterm"></a><a id="id-1.8.8.8.3.4.3" class="indexterm"></a><pre class="synopsis"> +RETURN NEXT <em class="replaceable"><code>expression</code></em>; +RETURN QUERY <em class="replaceable"><code>query</code></em>; +RETURN QUERY EXECUTE <em class="replaceable"><code>command-string</code></em> [<span class="optional"> USING <em class="replaceable"><code>expression</code></em> [<span class="optional">, ... </span>] </span>]; +</pre><p> + When a <span class="application">PL/pgSQL</span> function is declared to return + <code class="literal">SETOF <em class="replaceable"><code>sometype</code></em></code>, the procedure + to follow is slightly different. In that case, the individual + items to return are specified by a sequence of <code class="command">RETURN + NEXT</code> or <code class="command">RETURN QUERY</code> commands, and + then a final <code class="command">RETURN</code> command with no argument + is used to indicate that the function has finished executing. + <code class="command">RETURN NEXT</code> can be used with both scalar and + composite data types; with a composite result type, an entire + <span class="quote">“<span class="quote">table</span>”</span> of results will be returned. + <code class="command">RETURN QUERY</code> appends the results of executing + a query to the function's result set. <code class="command">RETURN + NEXT</code> and <code class="command">RETURN QUERY</code> can be freely + intermixed in a single set-returning function, in which case + their results will be concatenated. + </p><p> + <code class="command">RETURN NEXT</code> and <code class="command">RETURN + QUERY</code> do not actually return from the function — + they simply append zero or more rows to the function's result + set. Execution then continues with the next statement in the + <span class="application">PL/pgSQL</span> function. As successive + <code class="command">RETURN NEXT</code> or <code class="command">RETURN + QUERY</code> commands are executed, the result set is built + up. A final <code class="command">RETURN</code>, which should have no + argument, causes control to exit the function (or you can just + let control reach the end of the function). + </p><p> + <code class="command">RETURN QUERY</code> has a variant + <code class="command">RETURN QUERY EXECUTE</code>, which specifies the + query to be executed dynamically. Parameter expressions can + be inserted into the computed query string via <code class="literal">USING</code>, + in just the same way as in the <code class="command">EXECUTE</code> command. + </p><p> + If you declared the function with output parameters, write just + <code class="command">RETURN NEXT</code> with no expression. On each + execution, the current values of the output parameter + variable(s) will be saved for eventual return as a row of the + result. Note that you must declare the function as returning + <code class="literal">SETOF record</code> when there are multiple output + parameters, or <code class="literal">SETOF <em class="replaceable"><code>sometype</code></em></code> + when there is just one output parameter of type + <em class="replaceable"><code>sometype</code></em>, in order to create a set-returning + function with output parameters. + </p><p> + Here is an example of a function using <code class="command">RETURN + NEXT</code>: + +</p><pre class="programlisting"> +CREATE TABLE foo (fooid INT, foosubid INT, fooname TEXT); +INSERT INTO foo VALUES (1, 2, 'three'); +INSERT INTO foo VALUES (4, 5, 'six'); + +CREATE OR REPLACE FUNCTION get_all_foo() RETURNS SETOF foo AS +$BODY$ +DECLARE + r foo%rowtype; +BEGIN + FOR r IN + SELECT * FROM foo WHERE fooid > 0 + LOOP + -- can do some processing here + RETURN NEXT r; -- return current row of SELECT + END LOOP; + RETURN; +END; +$BODY$ +LANGUAGE plpgsql; + +SELECT * FROM get_all_foo(); +</pre><p> + </p><p> + Here is an example of a function using <code class="command">RETURN + QUERY</code>: + +</p><pre class="programlisting"> +CREATE FUNCTION get_available_flightid(date) RETURNS SETOF integer AS +$BODY$ +BEGIN + RETURN QUERY SELECT flightid + FROM flight + WHERE flightdate >= $1 + AND flightdate < ($1 + 1); + + -- Since execution is not finished, we can check whether rows were returned + -- and raise exception if not. + IF NOT FOUND THEN + RAISE EXCEPTION 'No flight at %.', $1; + END IF; + + RETURN; + END; +$BODY$ +LANGUAGE plpgsql; + +-- Returns available flights or raises exception if there are no +-- available flights. +SELECT * FROM get_available_flightid(CURRENT_DATE); +</pre><p> + </p><div class="note"><h3 class="title">Note</h3><p> + The current implementation of <code class="command">RETURN NEXT</code> + and <code class="command">RETURN QUERY</code> stores the entire result set + before returning from the function, as discussed above. That + means that if a <span class="application">PL/pgSQL</span> function produces a + very large result set, performance might be poor: data will be + written to disk to avoid memory exhaustion, but the function + itself will not return until the entire result set has been + generated. A future version of <span class="application">PL/pgSQL</span> might + allow users to define set-returning functions + that do not have this limitation. Currently, the point at + which data begins being written to disk is controlled by the + <a class="xref" href="runtime-config-resource.html#GUC-WORK-MEM">work_mem</a> + configuration variable. Administrators who have sufficient + memory to store larger result sets in memory should consider + increasing this parameter. + </p></div></div></div><div class="sect2" id="PLPGSQL-STATEMENTS-RETURNING-PROCEDURE"><div class="titlepage"><div><div><h3 class="title">43.6.2. Returning from a Procedure</h3></div></div></div><p> + A procedure does not have a return value. A procedure can therefore end + without a <code class="command">RETURN</code> statement. If you wish to use + a <code class="command">RETURN</code> statement to exit the code early, write + just <code class="command">RETURN</code> with no expression. + </p><p> + If the procedure has output parameters, the final values of the output + parameter variables will be returned to the caller. + </p></div><div class="sect2" id="PLPGSQL-STATEMENTS-CALLING-PROCEDURE"><div class="titlepage"><div><div><h3 class="title">43.6.3. Calling a Procedure</h3></div></div></div><p> + A <span class="application">PL/pgSQL</span> function, procedure, + or <code class="command">DO</code> block can call a procedure + using <code class="command">CALL</code>. Output parameters are handled + differently from the way that <code class="command">CALL</code> works in plain + SQL. Each <code class="literal">OUT</code> or <code class="literal">INOUT</code> + parameter of the procedure must + correspond to a variable in the <code class="command">CALL</code> statement, and + whatever the procedure returns is assigned back to that variable after + it returns. For example: +</p><pre class="programlisting"> +CREATE PROCEDURE triple(INOUT x int) +LANGUAGE plpgsql +AS $$ +BEGIN + x := x * 3; +END; +$$; + +DO $$ +DECLARE myvar int := 5; +BEGIN + CALL triple(myvar); + RAISE NOTICE 'myvar = %', myvar; -- prints 15 +END; +$$; +</pre><p> + The variable corresponding to an output parameter can be a simple + variable or a field of a composite-type variable. Currently, + it cannot be an element of an array. + </p></div><div class="sect2" id="PLPGSQL-CONDITIONALS"><div class="titlepage"><div><div><h3 class="title">43.6.4. Conditionals</h3></div></div></div><p> + <code class="command">IF</code> and <code class="command">CASE</code> statements let you execute + alternative commands based on certain conditions. + <span class="application">PL/pgSQL</span> has three forms of <code class="command">IF</code>: + </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">IF ... THEN ... END IF</code></p></li><li class="listitem"><p><code class="literal">IF ... THEN ... ELSE ... END IF</code></p></li><li class="listitem"><p><code class="literal">IF ... THEN ... ELSIF ... THEN ... ELSE ... END IF</code></p></li></ul></div><p> + + and two forms of <code class="command">CASE</code>: + </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">CASE ... WHEN ... THEN ... ELSE ... END CASE</code></p></li><li class="listitem"><p><code class="literal">CASE WHEN ... THEN ... ELSE ... END CASE</code></p></li></ul></div><p> + </p><div class="sect3" id="id-1.8.8.8.6.3"><div class="titlepage"><div><div><h4 class="title">43.6.4.1. <code class="literal">IF-THEN</code></h4></div></div></div><pre class="synopsis"> +IF <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> +END IF; +</pre><p> + <code class="literal">IF-THEN</code> statements are the simplest form of + <code class="literal">IF</code>. The statements between + <code class="literal">THEN</code> and <code class="literal">END IF</code> will be + executed if the condition is true. Otherwise, they are + skipped. + </p><p> + Example: +</p><pre class="programlisting"> +IF v_user_id <> 0 THEN + UPDATE users SET email = v_email WHERE user_id = v_user_id; +END IF; +</pre><p> + </p></div><div class="sect3" id="id-1.8.8.8.6.4"><div class="titlepage"><div><div><h4 class="title">43.6.4.2. <code class="literal">IF-THEN-ELSE</code></h4></div></div></div><pre class="synopsis"> +IF <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> +ELSE + <em class="replaceable"><code>statements</code></em> +END IF; +</pre><p> + <code class="literal">IF-THEN-ELSE</code> statements add to + <code class="literal">IF-THEN</code> by letting you specify an + alternative set of statements that should be executed if the + condition is not true. (Note this includes the case where the + condition evaluates to NULL.) + </p><p> + Examples: +</p><pre class="programlisting"> +IF parentid IS NULL OR parentid = '' +THEN + RETURN fullname; +ELSE + RETURN hp_true_filename(parentid) || '/' || fullname; +END IF; +</pre><p> + +</p><pre class="programlisting"> +IF v_count > 0 THEN + INSERT INTO users_count (count) VALUES (v_count); + RETURN 't'; +ELSE + RETURN 'f'; +END IF; +</pre><p> + </p></div><div class="sect3" id="id-1.8.8.8.6.5"><div class="titlepage"><div><div><h4 class="title">43.6.4.3. <code class="literal">IF-THEN-ELSIF</code></h4></div></div></div><pre class="synopsis"> +IF <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> +[<span class="optional"> ELSIF <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> +[<span class="optional"> ELSIF <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> + ... +</span>] +</span>] +[<span class="optional"> ELSE + <em class="replaceable"><code>statements</code></em> </span>] +END IF; +</pre><p> + Sometimes there are more than just two alternatives. + <code class="literal">IF-THEN-ELSIF</code> provides a convenient + method of checking several alternatives in turn. + The <code class="literal">IF</code> conditions are tested successively + until the first one that is true is found. Then the + associated statement(s) are executed, after which control + passes to the next statement after <code class="literal">END IF</code>. + (Any subsequent <code class="literal">IF</code> conditions are <span class="emphasis"><em>not</em></span> + tested.) If none of the <code class="literal">IF</code> conditions is true, + then the <code class="literal">ELSE</code> block (if any) is executed. + </p><p> + Here is an example: + +</p><pre class="programlisting"> +IF number = 0 THEN + result := 'zero'; +ELSIF number > 0 THEN + result := 'positive'; +ELSIF number < 0 THEN + result := 'negative'; +ELSE + -- hmm, the only other possibility is that number is null + result := 'NULL'; +END IF; +</pre><p> + </p><p> + The key word <code class="literal">ELSIF</code> can also be spelled + <code class="literal">ELSEIF</code>. + </p><p> + An alternative way of accomplishing the same task is to nest + <code class="literal">IF-THEN-ELSE</code> statements, as in the + following example: + +</p><pre class="programlisting"> +IF demo_row.sex = 'm' THEN + pretty_sex := 'man'; +ELSE + IF demo_row.sex = 'f' THEN + pretty_sex := 'woman'; + END IF; +END IF; +</pre><p> + </p><p> + However, this method requires writing a matching <code class="literal">END IF</code> + for each <code class="literal">IF</code>, so it is much more cumbersome than + using <code class="literal">ELSIF</code> when there are many alternatives. + </p></div><div class="sect3" id="id-1.8.8.8.6.6"><div class="titlepage"><div><div><h4 class="title">43.6.4.4. Simple <code class="literal">CASE</code></h4></div></div></div><pre class="synopsis"> +CASE <em class="replaceable"><code>search-expression</code></em> + WHEN <em class="replaceable"><code>expression</code></em> [<span class="optional">, <em class="replaceable"><code>expression</code></em> [<span class="optional"> ... </span>]</span>] THEN + <em class="replaceable"><code>statements</code></em> + [<span class="optional"> WHEN <em class="replaceable"><code>expression</code></em> [<span class="optional">, <em class="replaceable"><code>expression</code></em> [<span class="optional"> ... </span>]</span>] THEN + <em class="replaceable"><code>statements</code></em> + ... </span>] + [<span class="optional"> ELSE + <em class="replaceable"><code>statements</code></em> </span>] +END CASE; +</pre><p> + The simple form of <code class="command">CASE</code> provides conditional execution + based on equality of operands. The <em class="replaceable"><code>search-expression</code></em> + is evaluated (once) and successively compared to each + <em class="replaceable"><code>expression</code></em> in the <code class="literal">WHEN</code> clauses. + If a match is found, then the corresponding + <em class="replaceable"><code>statements</code></em> are executed, and then control + passes to the next statement after <code class="literal">END CASE</code>. (Subsequent + <code class="literal">WHEN</code> expressions are not evaluated.) If no match is + found, the <code class="literal">ELSE</code> <em class="replaceable"><code>statements</code></em> are + executed; but if <code class="literal">ELSE</code> is not present, then a + <code class="literal">CASE_NOT_FOUND</code> exception is raised. + </p><p> + Here is a simple example: + +</p><pre class="programlisting"> +CASE x + WHEN 1, 2 THEN + msg := 'one or two'; + ELSE + msg := 'other value than one or two'; +END CASE; +</pre><p> + </p></div><div class="sect3" id="id-1.8.8.8.6.7"><div class="titlepage"><div><div><h4 class="title">43.6.4.5. Searched <code class="literal">CASE</code></h4></div></div></div><pre class="synopsis"> +CASE + WHEN <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> + [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> THEN + <em class="replaceable"><code>statements</code></em> + ... </span>] + [<span class="optional"> ELSE + <em class="replaceable"><code>statements</code></em> </span>] +END CASE; +</pre><p> + The searched form of <code class="command">CASE</code> provides conditional execution + based on truth of Boolean expressions. Each <code class="literal">WHEN</code> clause's + <em class="replaceable"><code>boolean-expression</code></em> is evaluated in turn, + until one is found that yields <code class="literal">true</code>. Then the + corresponding <em class="replaceable"><code>statements</code></em> are executed, and + then control passes to the next statement after <code class="literal">END CASE</code>. + (Subsequent <code class="literal">WHEN</code> expressions are not evaluated.) + If no true result is found, the <code class="literal">ELSE</code> + <em class="replaceable"><code>statements</code></em> are executed; + but if <code class="literal">ELSE</code> is not present, then a + <code class="literal">CASE_NOT_FOUND</code> exception is raised. + </p><p> + Here is an example: + +</p><pre class="programlisting"> +CASE + WHEN x BETWEEN 0 AND 10 THEN + msg := 'value is between zero and ten'; + WHEN x BETWEEN 11 AND 20 THEN + msg := 'value is between eleven and twenty'; +END CASE; +</pre><p> + </p><p> + This form of <code class="command">CASE</code> is entirely equivalent to + <code class="literal">IF-THEN-ELSIF</code>, except for the rule that reaching + an omitted <code class="literal">ELSE</code> clause results in an error rather + than doing nothing. + </p></div></div><div class="sect2" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS"><div class="titlepage"><div><div><h3 class="title">43.6.5. Simple Loops</h3></div></div></div><a id="id-1.8.8.8.7.2" class="indexterm"></a><p> + With the <code class="literal">LOOP</code>, <code class="literal">EXIT</code>, + <code class="literal">CONTINUE</code>, <code class="literal">WHILE</code>, <code class="literal">FOR</code>, + and <code class="literal">FOREACH</code> statements, you can arrange for your + <span class="application">PL/pgSQL</span> function to repeat a series of commands. + </p><div class="sect3" id="id-1.8.8.8.7.4"><div class="titlepage"><div><div><h4 class="title">43.6.5.1. <code class="literal">LOOP</code></h4></div></div></div><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +LOOP + <em class="replaceable"><code>statements</code></em> +END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>]; +</pre><p> + <code class="literal">LOOP</code> defines an unconditional loop that is repeated + indefinitely until terminated by an <code class="literal">EXIT</code> or + <code class="command">RETURN</code> statement. The optional + <em class="replaceable"><code>label</code></em> can be used by <code class="literal">EXIT</code> + and <code class="literal">CONTINUE</code> statements within nested loops to + specify which loop those statements refer to. + </p></div><div class="sect3" id="id-1.8.8.8.7.5"><div class="titlepage"><div><div><h4 class="title">43.6.5.2. <code class="literal">EXIT</code></h4></div></div></div><a id="id-1.8.8.8.7.5.2" class="indexterm"></a><pre class="synopsis"> +EXIT [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>] [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> </span>]; +</pre><p> + If no <em class="replaceable"><code>label</code></em> is given, the innermost + loop is terminated and the statement following <code class="literal">END + LOOP</code> is executed next. If <em class="replaceable"><code>label</code></em> + is given, it must be the label of the current or some outer + level of nested loop or block. Then the named loop or block is + terminated and control continues with the statement after the + loop's/block's corresponding <code class="literal">END</code>. + </p><p> + If <code class="literal">WHEN</code> is specified, the loop exit occurs only if + <em class="replaceable"><code>boolean-expression</code></em> is true. Otherwise, control passes + to the statement after <code class="literal">EXIT</code>. + </p><p> + <code class="literal">EXIT</code> can be used with all types of loops; it is + not limited to use with unconditional loops. + </p><p> + When used with a + <code class="literal">BEGIN</code> block, <code class="literal">EXIT</code> passes + control to the next statement after the end of the block. + Note that a label must be used for this purpose; an unlabeled + <code class="literal">EXIT</code> is never considered to match a + <code class="literal">BEGIN</code> block. (This is a change from + pre-8.4 releases of <span class="productname">PostgreSQL</span>, which + would allow an unlabeled <code class="literal">EXIT</code> to match + a <code class="literal">BEGIN</code> block.) + </p><p> + Examples: +</p><pre class="programlisting"> +LOOP + -- some computations + IF count > 0 THEN + EXIT; -- exit loop + END IF; +END LOOP; + +LOOP + -- some computations + EXIT WHEN count > 0; -- same result as previous example +END LOOP; + +<<ablock>> +BEGIN + -- some computations + IF stocks > 100000 THEN + EXIT ablock; -- causes exit from the BEGIN block + END IF; + -- computations here will be skipped when stocks > 100000 +END; +</pre><p> + </p></div><div class="sect3" id="id-1.8.8.8.7.6"><div class="titlepage"><div><div><h4 class="title">43.6.5.3. <code class="literal">CONTINUE</code></h4></div></div></div><a id="id-1.8.8.8.7.6.2" class="indexterm"></a><pre class="synopsis"> +CONTINUE [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>] [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> </span>]; +</pre><p> + If no <em class="replaceable"><code>label</code></em> is given, the next iteration of + the innermost loop is begun. That is, all statements remaining + in the loop body are skipped, and control returns + to the loop control expression (if any) to determine whether + another loop iteration is needed. + If <em class="replaceable"><code>label</code></em> is present, it + specifies the label of the loop whose execution will be + continued. + </p><p> + If <code class="literal">WHEN</code> is specified, the next iteration of the + loop is begun only if <em class="replaceable"><code>boolean-expression</code></em> is + true. Otherwise, control passes to the statement after + <code class="literal">CONTINUE</code>. + </p><p> + <code class="literal">CONTINUE</code> can be used with all types of loops; it + is not limited to use with unconditional loops. + </p><p> + Examples: +</p><pre class="programlisting"> +LOOP + -- some computations + EXIT WHEN count > 100; + CONTINUE WHEN count < 50; + -- some computations for count IN [50 .. 100] +END LOOP; +</pre><p> + </p></div><div class="sect3" id="id-1.8.8.8.7.7"><div class="titlepage"><div><div><h4 class="title">43.6.5.4. <code class="literal">WHILE</code></h4></div></div></div><a id="id-1.8.8.8.7.7.2" class="indexterm"></a><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +WHILE <em class="replaceable"><code>boolean-expression</code></em> LOOP + <em class="replaceable"><code>statements</code></em> +END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>]; +</pre><p> + The <code class="literal">WHILE</code> statement repeats a + sequence of statements so long as the + <em class="replaceable"><code>boolean-expression</code></em> + evaluates to true. The expression is checked just before + each entry to the loop body. + </p><p> + For example: +</p><pre class="programlisting"> +WHILE amount_owed > 0 AND gift_certificate_balance > 0 LOOP + -- some computations here +END LOOP; + +WHILE NOT done LOOP + -- some computations here +END LOOP; +</pre><p> + </p></div><div class="sect3" id="PLPGSQL-INTEGER-FOR"><div class="titlepage"><div><div><h4 class="title">43.6.5.5. <code class="literal">FOR</code> (Integer Variant)</h4></div></div></div><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +FOR <em class="replaceable"><code>name</code></em> IN [<span class="optional"> REVERSE </span>] <em class="replaceable"><code>expression</code></em> .. <em class="replaceable"><code>expression</code></em> [<span class="optional"> BY <em class="replaceable"><code>expression</code></em> </span>] LOOP + <em class="replaceable"><code>statements</code></em> +END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>]; +</pre><p> + This form of <code class="literal">FOR</code> creates a loop that iterates over a range + of integer values. The variable + <em class="replaceable"><code>name</code></em> is automatically defined as type + <code class="type">integer</code> and exists only inside the loop (any existing + definition of the variable name is ignored within the loop). + The two expressions giving + the lower and upper bound of the range are evaluated once when entering + the loop. If the <code class="literal">BY</code> clause isn't specified the iteration + step is 1, otherwise it's the value specified in the <code class="literal">BY</code> + clause, which again is evaluated once on loop entry. + If <code class="literal">REVERSE</code> is specified then the step value is + subtracted, rather than added, after each iteration. + </p><p> + Some examples of integer <code class="literal">FOR</code> loops: +</p><pre class="programlisting"> +FOR i IN 1..10 LOOP + -- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop +END LOOP; + +FOR i IN REVERSE 10..1 LOOP + -- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop +END LOOP; + +FOR i IN REVERSE 10..1 BY 2 LOOP + -- i will take on the values 10,8,6,4,2 within the loop +END LOOP; +</pre><p> + </p><p> + If the lower bound is greater than the upper bound (or less than, + in the <code class="literal">REVERSE</code> case), the loop body is not + executed at all. No error is raised. + </p><p> + If a <em class="replaceable"><code>label</code></em> is attached to the + <code class="literal">FOR</code> loop then the integer loop variable can be + referenced with a qualified name, using that + <em class="replaceable"><code>label</code></em>. + </p></div></div><div class="sect2" id="PLPGSQL-RECORDS-ITERATING"><div class="titlepage"><div><div><h3 class="title">43.6.6. Looping through Query Results</h3></div></div></div><p> + Using a different type of <code class="literal">FOR</code> loop, you can iterate through + the results of a query and manipulate that data + accordingly. The syntax is: +</p><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +FOR <em class="replaceable"><code>target</code></em> IN <em class="replaceable"><code>query</code></em> LOOP + <em class="replaceable"><code>statements</code></em> +END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>]; +</pre><p> + The <em class="replaceable"><code>target</code></em> is a record variable, row variable, + or comma-separated list of scalar variables. + The <em class="replaceable"><code>target</code></em> is successively assigned each row + resulting from the <em class="replaceable"><code>query</code></em> and the loop body is + executed for each row. Here is an example: +</p><pre class="programlisting"> +CREATE FUNCTION refresh_mviews() RETURNS integer AS $$ +DECLARE + mviews RECORD; +BEGIN + RAISE NOTICE 'Refreshing all materialized views...'; + + FOR mviews IN + SELECT n.nspname AS mv_schema, + c.relname AS mv_name, + pg_catalog.pg_get_userbyid(c.relowner) AS owner + FROM pg_catalog.pg_class c + LEFT JOIN pg_catalog.pg_namespace n ON (n.oid = c.relnamespace) + WHERE c.relkind = 'm' + ORDER BY 1 + LOOP + + -- Now "mviews" has one record with information about the materialized view + + RAISE NOTICE 'Refreshing materialized view %.% (owner: %)...', + quote_ident(mviews.mv_schema), + quote_ident(mviews.mv_name), + quote_ident(mviews.owner); + EXECUTE format('REFRESH MATERIALIZED VIEW %I.%I', mviews.mv_schema, mviews.mv_name); + END LOOP; + + RAISE NOTICE 'Done refreshing materialized views.'; + RETURN 1; +END; +$$ LANGUAGE plpgsql; +</pre><p> + + If the loop is terminated by an <code class="literal">EXIT</code> statement, the last + assigned row value is still accessible after the loop. + </p><p> + The <em class="replaceable"><code>query</code></em> used in this type of <code class="literal">FOR</code> + statement can be any SQL command that returns rows to the caller: + <code class="command">SELECT</code> is the most common case, + but you can also use <code class="command">INSERT</code>, <code class="command">UPDATE</code>, or + <code class="command">DELETE</code> with a <code class="literal">RETURNING</code> clause. Some utility + commands such as <code class="command">EXPLAIN</code> will work too. + </p><p> + <span class="application">PL/pgSQL</span> variables are replaced by query parameters, + and the query plan is cached for possible re-use, as discussed in + detail in <a class="xref" href="plpgsql-implementation.html#PLPGSQL-VAR-SUBST" title="43.11.1. Variable Substitution">Section 43.11.1</a> and + <a class="xref" href="plpgsql-implementation.html#PLPGSQL-PLAN-CACHING" title="43.11.2. Plan Caching">Section 43.11.2</a>. + </p><p> + The <code class="literal">FOR-IN-EXECUTE</code> statement is another way to iterate over + rows: +</p><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +FOR <em class="replaceable"><code>target</code></em> IN EXECUTE <em class="replaceable"><code>text_expression</code></em> [<span class="optional"> USING <em class="replaceable"><code>expression</code></em> [<span class="optional">, ... </span>] </span>] LOOP + <em class="replaceable"><code>statements</code></em> +END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>]; +</pre><p> + This is like the previous form, except that the source query + is specified as a string expression, which is evaluated and replanned + on each entry to the <code class="literal">FOR</code> loop. This allows the programmer to + choose the speed of a preplanned query or the flexibility of a dynamic + query, just as with a plain <code class="command">EXECUTE</code> statement. + As with <code class="command">EXECUTE</code>, parameter values can be inserted + into the dynamic command via <code class="literal">USING</code>. + </p><p> + Another way to specify the query whose results should be iterated + through is to declare it as a cursor. This is described in + <a class="xref" href="plpgsql-cursors.html#PLPGSQL-CURSOR-FOR-LOOP" title="43.7.4. Looping through a Cursor's Result">Section 43.7.4</a>. + </p></div><div class="sect2" id="PLPGSQL-FOREACH-ARRAY"><div class="titlepage"><div><div><h3 class="title">43.6.7. Looping through Arrays</h3></div></div></div><p> + The <code class="literal">FOREACH</code> loop is much like a <code class="literal">FOR</code> loop, + but instead of iterating through the rows returned by an SQL query, + it iterates through the elements of an array value. + (In general, <code class="literal">FOREACH</code> is meant for looping through + components of a composite-valued expression; variants for looping + through composites besides arrays may be added in future.) + The <code class="literal">FOREACH</code> statement to loop over an array is: + +</p><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +FOREACH <em class="replaceable"><code>target</code></em> [<span class="optional"> SLICE <em class="replaceable"><code>number</code></em> </span>] IN ARRAY <em class="replaceable"><code>expression</code></em> LOOP + <em class="replaceable"><code>statements</code></em> +END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>]; +</pre><p> + </p><p> + Without <code class="literal">SLICE</code>, or if <code class="literal">SLICE 0</code> is specified, + the loop iterates through individual elements of the array produced + by evaluating the <em class="replaceable"><code>expression</code></em>. + The <em class="replaceable"><code>target</code></em> variable is assigned each + element value in sequence, and the loop body is executed for each element. + Here is an example of looping through the elements of an integer + array: + +</p><pre class="programlisting"> +CREATE FUNCTION sum(int[]) RETURNS int8 AS $$ +DECLARE + s int8 := 0; + x int; +BEGIN + FOREACH x IN ARRAY $1 + LOOP + s := s + x; + END LOOP; + RETURN s; +END; +$$ LANGUAGE plpgsql; +</pre><p> + + The elements are visited in storage order, regardless of the number of + array dimensions. Although the <em class="replaceable"><code>target</code></em> is + usually just a single variable, it can be a list of variables when + looping through an array of composite values (records). In that case, + for each array element, the variables are assigned from successive + columns of the composite value. + </p><p> + With a positive <code class="literal">SLICE</code> value, <code class="literal">FOREACH</code> + iterates through slices of the array rather than single elements. + The <code class="literal">SLICE</code> value must be an integer constant not larger + than the number of dimensions of the array. The + <em class="replaceable"><code>target</code></em> variable must be an array, + and it receives successive slices of the array value, where each slice + is of the number of dimensions specified by <code class="literal">SLICE</code>. + Here is an example of iterating through one-dimensional slices: + +</p><pre class="programlisting"> +CREATE FUNCTION scan_rows(int[]) RETURNS void AS $$ +DECLARE + x int[]; +BEGIN + FOREACH x SLICE 1 IN ARRAY $1 + LOOP + RAISE NOTICE 'row = %', x; + END LOOP; +END; +$$ LANGUAGE plpgsql; + +SELECT scan_rows(ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]); + +NOTICE: row = {1,2,3} +NOTICE: row = {4,5,6} +NOTICE: row = {7,8,9} +NOTICE: row = {10,11,12} +</pre><p> + </p></div><div class="sect2" id="PLPGSQL-ERROR-TRAPPING"><div class="titlepage"><div><div><h3 class="title">43.6.8. Trapping Errors</h3></div></div></div><a id="id-1.8.8.8.10.2" class="indexterm"></a><p> + By default, any error occurring in a <span class="application">PL/pgSQL</span> + function aborts execution of the function and the + surrounding transaction. You can trap errors and recover + from them by using a <code class="command">BEGIN</code> block with an + <code class="literal">EXCEPTION</code> clause. The syntax is an extension of the + normal syntax for a <code class="command">BEGIN</code> block: + +</p><pre class="synopsis"> +[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>] +[<span class="optional"> DECLARE + <em class="replaceable"><code>declarations</code></em> </span>] +BEGIN + <em class="replaceable"><code>statements</code></em> +EXCEPTION + WHEN <em class="replaceable"><code>condition</code></em> [<span class="optional"> OR <em class="replaceable"><code>condition</code></em> ... </span>] THEN + <em class="replaceable"><code>handler_statements</code></em> + [<span class="optional"> WHEN <em class="replaceable"><code>condition</code></em> [<span class="optional"> OR <em class="replaceable"><code>condition</code></em> ... </span>] THEN + <em class="replaceable"><code>handler_statements</code></em> + ... </span>] +END; +</pre><p> + </p><p> + If no error occurs, this form of block simply executes all the + <em class="replaceable"><code>statements</code></em>, and then control passes + to the next statement after <code class="literal">END</code>. But if an error + occurs within the <em class="replaceable"><code>statements</code></em>, further + processing of the <em class="replaceable"><code>statements</code></em> is + abandoned, and control passes to the <code class="literal">EXCEPTION</code> list. + The list is searched for the first <em class="replaceable"><code>condition</code></em> + matching the error that occurred. If a match is found, the + corresponding <em class="replaceable"><code>handler_statements</code></em> are + executed, and then control passes to the next statement after + <code class="literal">END</code>. If no match is found, the error propagates out + as though the <code class="literal">EXCEPTION</code> clause were not there at all: + the error can be caught by an enclosing block with + <code class="literal">EXCEPTION</code>, or if there is none it aborts processing + of the function. + </p><p> + The <em class="replaceable"><code>condition</code></em> names can be any of + those shown in <a class="xref" href="errcodes-appendix.html" title="Appendix A. PostgreSQL Error Codes">Appendix A</a>. A category + name matches any error within its category. The special + condition name <code class="literal">OTHERS</code> matches every error type except + <code class="literal">QUERY_CANCELED</code> and <code class="literal">ASSERT_FAILURE</code>. + (It is possible, but often unwise, to trap those two error types + by name.) Condition names are + not case-sensitive. Also, an error condition can be specified + by <code class="literal">SQLSTATE</code> code; for example these are equivalent: +</p><pre class="programlisting"> +WHEN division_by_zero THEN ... +WHEN SQLSTATE '22012' THEN ... +</pre><p> + </p><p> + If a new error occurs within the selected + <em class="replaceable"><code>handler_statements</code></em>, it cannot be caught + by this <code class="literal">EXCEPTION</code> clause, but is propagated out. + A surrounding <code class="literal">EXCEPTION</code> clause could catch it. + </p><p> + When an error is caught by an <code class="literal">EXCEPTION</code> clause, + the local variables of the <span class="application">PL/pgSQL</span> function + remain as they were when the error occurred, but all changes + to persistent database state within the block are rolled back. + As an example, consider this fragment: + +</p><pre class="programlisting"> +INSERT INTO mytab(firstname, lastname) VALUES('Tom', 'Jones'); +BEGIN + UPDATE mytab SET firstname = 'Joe' WHERE lastname = 'Jones'; + x := x + 1; + y := x / 0; +EXCEPTION + WHEN division_by_zero THEN + RAISE NOTICE 'caught division_by_zero'; + RETURN x; +END; +</pre><p> + + When control reaches the assignment to <code class="literal">y</code>, it will + fail with a <code class="literal">division_by_zero</code> error. This will be caught by + the <code class="literal">EXCEPTION</code> clause. The value returned in the + <code class="command">RETURN</code> statement will be the incremented value of + <code class="literal">x</code>, but the effects of the <code class="command">UPDATE</code> command will + have been rolled back. The <code class="command">INSERT</code> command preceding the + block is not rolled back, however, so the end result is that the database + contains <code class="literal">Tom Jones</code> not <code class="literal">Joe Jones</code>. + </p><div class="tip"><h3 class="title">Tip</h3><p> + A block containing an <code class="literal">EXCEPTION</code> clause is significantly + more expensive to enter and exit than a block without one. Therefore, + don't use <code class="literal">EXCEPTION</code> without need. + </p></div><div class="example" id="PLPGSQL-UPSERT-EXAMPLE"><p class="title"><strong>Example 43.2. Exceptions with <code class="command">UPDATE</code>/<code class="command">INSERT</code></strong></p><div class="example-contents"><p> + + This example uses exception handling to perform either + <code class="command">UPDATE</code> or <code class="command">INSERT</code>, as appropriate. It is + recommended that applications use <code class="command">INSERT</code> with + <code class="literal">ON CONFLICT DO UPDATE</code> rather than actually using + this pattern. This example serves primarily to illustrate use of + <span class="application">PL/pgSQL</span> control flow structures: + +</p><pre class="programlisting"> +CREATE TABLE db (a INT PRIMARY KEY, b TEXT); + +CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS +$$ +BEGIN + LOOP + -- first try to update the key + UPDATE db SET b = data WHERE a = key; + IF found THEN + RETURN; + END IF; + -- not there, so try to insert the key + -- if someone else inserts the same key concurrently, + -- we could get a unique-key failure + BEGIN + INSERT INTO db(a,b) VALUES (key, data); + RETURN; + EXCEPTION WHEN unique_violation THEN + -- Do nothing, and loop to try the UPDATE again. + END; + END LOOP; +END; +$$ +LANGUAGE plpgsql; + +SELECT merge_db(1, 'david'); +SELECT merge_db(1, 'dennis'); +</pre><p> + + This coding assumes the <code class="literal">unique_violation</code> error is caused by + the <code class="command">INSERT</code>, and not by, say, an <code class="command">INSERT</code> in a + trigger function on the table. It might also misbehave if there is + more than one unique index on the table, since it will retry the + operation regardless of which index caused the error. + More safety could be had by using the + features discussed next to check that the trapped error was the one + expected. + </p></div></div><br class="example-break" /><div class="sect3" id="PLPGSQL-EXCEPTION-DIAGNOSTICS"><div class="titlepage"><div><div><h4 class="title">43.6.8.1. Obtaining Information about an Error</h4></div></div></div><p> + Exception handlers frequently need to identify the specific error that + occurred. There are two ways to get information about the current + exception in <span class="application">PL/pgSQL</span>: special variables and the + <code class="command">GET STACKED DIAGNOSTICS</code> command. + </p><p> + Within an exception handler, the special variable + <code class="varname">SQLSTATE</code> contains the error code that corresponds to + the exception that was raised (refer to <a class="xref" href="errcodes-appendix.html#ERRCODES-TABLE" title="Table A.1. PostgreSQL Error Codes">Table A.1</a> + for a list of possible error codes). The special variable + <code class="varname">SQLERRM</code> contains the error message associated with the + exception. These variables are undefined outside exception handlers. + </p><p> + Within an exception handler, one may also retrieve + information about the current exception by using the + <code class="command">GET STACKED DIAGNOSTICS</code> command, which has the form: + +</p><pre class="synopsis"> +GET STACKED DIAGNOSTICS <em class="replaceable"><code>variable</code></em> { = | := } <em class="replaceable"><code>item</code></em> [<span class="optional"> , ... </span>]; +</pre><p> + + Each <em class="replaceable"><code>item</code></em> is a key word identifying a status + value to be assigned to the specified <em class="replaceable"><code>variable</code></em> + (which should be of the right data type to receive it). The currently + available status items are shown + in <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-EXCEPTION-DIAGNOSTICS-VALUES" title="Table 43.2. Error Diagnostics Items">Table 43.2</a>. + </p><div class="table" id="PLPGSQL-EXCEPTION-DIAGNOSTICS-VALUES"><p class="title"><strong>Table 43.2. Error Diagnostics Items</strong></p><div class="table-contents"><table class="table" summary="Error Diagnostics Items" border="1"><colgroup><col class="col1" /><col class="col2" /><col class="col3" /></colgroup><thead><tr><th>Name</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal">RETURNED_SQLSTATE</code></td><td><code class="type">text</code></td><td>the SQLSTATE error code of the exception</td></tr><tr><td><code class="literal">COLUMN_NAME</code></td><td><code class="type">text</code></td><td>the name of the column related to exception</td></tr><tr><td><code class="literal">CONSTRAINT_NAME</code></td><td><code class="type">text</code></td><td>the name of the constraint related to exception</td></tr><tr><td><code class="literal">PG_DATATYPE_NAME</code></td><td><code class="type">text</code></td><td>the name of the data type related to exception</td></tr><tr><td><code class="literal">MESSAGE_TEXT</code></td><td><code class="type">text</code></td><td>the text of the exception's primary message</td></tr><tr><td><code class="literal">TABLE_NAME</code></td><td><code class="type">text</code></td><td>the name of the table related to exception</td></tr><tr><td><code class="literal">SCHEMA_NAME</code></td><td><code class="type">text</code></td><td>the name of the schema related to exception</td></tr><tr><td><code class="literal">PG_EXCEPTION_DETAIL</code></td><td><code class="type">text</code></td><td>the text of the exception's detail message, if any</td></tr><tr><td><code class="literal">PG_EXCEPTION_HINT</code></td><td><code class="type">text</code></td><td>the text of the exception's hint message, if any</td></tr><tr><td><code class="literal">PG_EXCEPTION_CONTEXT</code></td><td><code class="type">text</code></td><td>line(s) of text describing the call stack at the time of the + exception (see <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-CALL-STACK" title="43.6.9. Obtaining Execution Location Information">Section 43.6.9</a>)</td></tr></tbody></table></div></div><br class="table-break" /><p> + If the exception did not set a value for an item, an empty string + will be returned. + </p><p> + Here is an example: +</p><pre class="programlisting"> +DECLARE + text_var1 text; + text_var2 text; + text_var3 text; +BEGIN + -- some processing which might cause an exception + ... +EXCEPTION WHEN OTHERS THEN + GET STACKED DIAGNOSTICS text_var1 = MESSAGE_TEXT, + text_var2 = PG_EXCEPTION_DETAIL, + text_var3 = PG_EXCEPTION_HINT; +END; +</pre><p> + </p></div></div><div class="sect2" id="PLPGSQL-CALL-STACK"><div class="titlepage"><div><div><h3 class="title">43.6.9. Obtaining Execution Location Information</h3></div></div></div><p> + The <code class="command">GET DIAGNOSTICS</code> command, previously described + in <a class="xref" href="plpgsql-statements.html#PLPGSQL-STATEMENTS-DIAGNOSTICS" title="43.5.5. Obtaining the Result Status">Section 43.5.5</a>, retrieves information + about current execution state (whereas the <code class="command">GET STACKED + DIAGNOSTICS</code> command discussed above reports information about + the execution state as of a previous error). Its <code class="literal">PG_CONTEXT</code> + status item is useful for identifying the current execution + location. <code class="literal">PG_CONTEXT</code> returns a text string with line(s) + of text describing the call stack. The first line refers to the current + function and currently executing <code class="command">GET DIAGNOSTICS</code> + command. The second and any subsequent lines refer to calling functions + further up the call stack. For example: + +</p><pre class="programlisting"> +CREATE OR REPLACE FUNCTION outer_func() RETURNS integer AS $$ +BEGIN + RETURN inner_func(); +END; +$$ LANGUAGE plpgsql; + +CREATE OR REPLACE FUNCTION inner_func() RETURNS integer AS $$ +DECLARE + stack text; +BEGIN + GET DIAGNOSTICS stack = PG_CONTEXT; + RAISE NOTICE E'--- Call Stack ---\n%', stack; + RETURN 1; +END; +$$ LANGUAGE plpgsql; + +SELECT outer_func(); + +NOTICE: --- Call Stack --- +PL/pgSQL function inner_func() line 5 at GET DIAGNOSTICS +PL/pgSQL function outer_func() line 3 at RETURN +CONTEXT: PL/pgSQL function outer_func() line 3 at RETURN + outer_func + ------------ + 1 +(1 row) +</pre><p> + + </p><p> + <code class="literal">GET STACKED DIAGNOSTICS ... PG_EXCEPTION_CONTEXT</code> + returns the same sort of stack trace, but describing the location + at which an error was detected, rather than the current location. + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpgsql-statements.html" title="43.5. Basic Statements">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpgsql.html" title="Chapter 43. PL/pgSQL — SQL Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpgsql-cursors.html" title="43.7. Cursors">Next</a></td></tr><tr><td width="40%" align="left" valign="top">43.5. Basic Statements </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 43.7. Cursors</td></tr></table></div></body></html>
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