diff options
Diffstat (limited to 'doc/src/sgml/html/sql-syntax-calling-funcs.html')
| -rw-r--r-- | doc/src/sgml/html/sql-syntax-calling-funcs.html | 132 |
1 files changed, 132 insertions, 0 deletions
diff --git a/doc/src/sgml/html/sql-syntax-calling-funcs.html b/doc/src/sgml/html/sql-syntax-calling-funcs.html new file mode 100644 index 0000000..0280dd2 --- /dev/null +++ b/doc/src/sgml/html/sql-syntax-calling-funcs.html @@ -0,0 +1,132 @@ +<?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>4.3. Calling Functions</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="sql-expressions.html" title="4.2. Value Expressions" /><link rel="next" href="ddl.html" title="Chapter 5. Data Definition" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">4.3. Calling Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-expressions.html" title="4.2. Value Expressions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-syntax.html" title="Chapter 4. SQL Syntax">Up</a></td><th width="60%" align="center">Chapter 4. SQL Syntax</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ddl.html" title="Chapter 5. Data Definition">Next</a></td></tr></table><hr /></div><div class="sect1" id="SQL-SYNTAX-CALLING-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">4.3. Calling Functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-POSITIONAL">4.3.1. Using Positional Notation</a></span></dt><dt><span class="sect2"><a href="sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-NAMED">4.3.2. Using Named Notation</a></span></dt><dt><span class="sect2"><a href="sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-MIXED">4.3.3. Using Mixed Notation</a></span></dt></dl></div><a id="id-1.5.3.7.2" class="indexterm"></a><p> + <span class="productname">PostgreSQL</span> allows functions that have named + parameters to be called using either <em class="firstterm">positional</em> or + <em class="firstterm">named</em> notation. Named notation is especially + useful for functions that have a large number of parameters, since it + makes the associations between parameters and actual arguments more + explicit and reliable. + In positional notation, a function call is written with + its argument values in the same order as they are defined in the function + declaration. In named notation, the arguments are matched to the + function parameters by name and can be written in any order. + For each notation, also consider the effect of function argument types, + documented in <a class="xref" href="typeconv-func.html" title="10.3. Functions">Section 10.3</a>. + </p><p> + In either notation, parameters that have default values given in the + function declaration need not be written in the call at all. But this + is particularly useful in named notation, since any combination of + parameters can be omitted; while in positional notation parameters can + only be omitted from right to left. + </p><p> + <span class="productname">PostgreSQL</span> also supports + <em class="firstterm">mixed</em> notation, which combines positional and + named notation. In this case, positional parameters are written first + and named parameters appear after them. + </p><p> + The following examples will illustrate the usage of all three + notations, using the following function definition: +</p><pre class="programlisting"> +CREATE FUNCTION concat_lower_or_upper(a text, b text, uppercase boolean DEFAULT false) +RETURNS text +AS +$$ + SELECT CASE + WHEN $3 THEN UPPER($1 || ' ' || $2) + ELSE LOWER($1 || ' ' || $2) + END; +$$ +LANGUAGE SQL IMMUTABLE STRICT; +</pre><p> + Function <code class="function">concat_lower_or_upper</code> has two mandatory + parameters, <code class="literal">a</code> and <code class="literal">b</code>. Additionally + there is one optional parameter <code class="literal">uppercase</code> which defaults + to <code class="literal">false</code>. The <code class="literal">a</code> and + <code class="literal">b</code> inputs will be concatenated, and forced to either + upper or lower case depending on the <code class="literal">uppercase</code> + parameter. The remaining details of this function + definition are not important here (see <a class="xref" href="extend.html" title="Chapter 38. Extending SQL">Chapter 38</a> for + more information). + </p><div class="sect2" id="SQL-SYNTAX-CALLING-FUNCS-POSITIONAL"><div class="titlepage"><div><div><h3 class="title">4.3.1. Using Positional Notation</h3></div></div></div><a id="id-1.5.3.7.7.2" class="indexterm"></a><p> + Positional notation is the traditional mechanism for passing arguments + to functions in <span class="productname">PostgreSQL</span>. An example is: +</p><pre class="screen"> +SELECT concat_lower_or_upper('Hello', 'World', true); + concat_lower_or_upper +----------------------- + HELLO WORLD +(1 row) +</pre><p> + All arguments are specified in order. The result is upper case since + <code class="literal">uppercase</code> is specified as <code class="literal">true</code>. + Another example is: +</p><pre class="screen"> +SELECT concat_lower_or_upper('Hello', 'World'); + concat_lower_or_upper +----------------------- + hello world +(1 row) +</pre><p> + Here, the <code class="literal">uppercase</code> parameter is omitted, so it + receives its default value of <code class="literal">false</code>, resulting in + lower case output. In positional notation, arguments can be omitted + from right to left so long as they have defaults. + </p></div><div class="sect2" id="SQL-SYNTAX-CALLING-FUNCS-NAMED"><div class="titlepage"><div><div><h3 class="title">4.3.2. Using Named Notation</h3></div></div></div><a id="id-1.5.3.7.8.2" class="indexterm"></a><p> + In named notation, each argument's name is specified using + <code class="literal">=></code> to separate it from the argument expression. + For example: +</p><pre class="screen"> +SELECT concat_lower_or_upper(a => 'Hello', b => 'World'); + concat_lower_or_upper +----------------------- + hello world +(1 row) +</pre><p> + Again, the argument <code class="literal">uppercase</code> was omitted + so it is set to <code class="literal">false</code> implicitly. One advantage of + using named notation is that the arguments may be specified in any + order, for example: +</p><pre class="screen"> +SELECT concat_lower_or_upper(a => 'Hello', b => 'World', uppercase => true); + concat_lower_or_upper +----------------------- + HELLO WORLD +(1 row) + +SELECT concat_lower_or_upper(a => 'Hello', uppercase => true, b => 'World'); + concat_lower_or_upper +----------------------- + HELLO WORLD +(1 row) +</pre><p> + </p><p> + An older syntax based on ":=" is supported for backward compatibility: +</p><pre class="screen"> +SELECT concat_lower_or_upper(a := 'Hello', uppercase := true, b := 'World'); + concat_lower_or_upper +----------------------- + HELLO WORLD +(1 row) +</pre><p> + </p></div><div class="sect2" id="SQL-SYNTAX-CALLING-FUNCS-MIXED"><div class="titlepage"><div><div><h3 class="title">4.3.3. Using Mixed Notation</h3></div></div></div><a id="id-1.5.3.7.9.2" class="indexterm"></a><p> + The mixed notation combines positional and named notation. However, as + already mentioned, named arguments cannot precede positional arguments. + For example: +</p><pre class="screen"> +SELECT concat_lower_or_upper('Hello', 'World', uppercase => true); + concat_lower_or_upper +----------------------- + HELLO WORLD +(1 row) +</pre><p> + In the above query, the arguments <code class="literal">a</code> and + <code class="literal">b</code> are specified positionally, while + <code class="literal">uppercase</code> is specified by name. In this example, + that adds little except documentation. With a more complex function + having numerous parameters that have default values, named or mixed + notation can save a great deal of writing and reduce chances for error. + </p><div class="note"><h3 class="title">Note</h3><p> + Named and mixed call notations currently cannot be used when calling an + aggregate function (but they do work when an aggregate function is used + as a window function). + </p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-expressions.html" title="4.2. Value Expressions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-syntax.html" title="Chapter 4. SQL Syntax">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ddl.html" title="Chapter 5. Data Definition">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4.2. Value Expressions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 5. Data Definition</td></tr></table></div></body></html>
\ No newline at end of file |