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diff --git a/doc/src/sgml/html/functions-window.html b/doc/src/sgml/html/functions-window.html new file mode 100644 index 0000000..d5c9047 --- /dev/null +++ b/doc/src/sgml/html/functions-window.html @@ -0,0 +1,182 @@ +<?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>9.22. Window 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 V1.79.1" /><link rel="prev" href="functions-aggregate.html" title="9.21. Aggregate Functions" /><link rel="next" href="functions-subquery.html" title="9.23. Subquery Expressions" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.22. Window Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-aggregate.html" title="9.21. Aggregate Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-subquery.html" title="9.23. Subquery Expressions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-WINDOW"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.22. Window Functions</h2></div></div></div><a id="id-1.5.8.28.2" class="indexterm"></a><p> + <em class="firstterm">Window functions</em> provide the ability to perform + calculations across sets of rows that are related to the current query + row. See <a class="xref" href="tutorial-window.html" title="3.5. Window Functions">Section 3.5</a> for an introduction to this + feature, and <a class="xref" href="sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS" title="4.2.8. Window Function Calls">Section 4.2.8</a> for syntax + details. + </p><p> + The built-in window functions are listed in + <a class="xref" href="functions-window.html#FUNCTIONS-WINDOW-TABLE" title="Table 9.60. General-Purpose Window Functions">Table 9.60</a>. Note that these functions + <span class="emphasis"><em>must</em></span> be invoked using window function syntax, i.e., an + <code class="literal">OVER</code> clause is required. + </p><p> + In addition to these functions, any built-in or user-defined + ordinary aggregate (i.e., not ordered-set or hypothetical-set aggregates) + can be used as a window function; see + <a class="xref" href="functions-aggregate.html" title="9.21. Aggregate Functions">Section 9.21</a> for a list of the built-in aggregates. + Aggregate functions act as window functions only when an <code class="literal">OVER</code> + clause follows the call; otherwise they act as plain aggregates + and return a single row for the entire set. + </p><div class="table" id="FUNCTIONS-WINDOW-TABLE"><p class="title"><strong>Table 9.60. General-Purpose Window Functions</strong></p><div class="table-contents"><table class="table" summary="General-Purpose Window Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature"> + Function + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.1.1.1.1" class="indexterm"></a> + <code class="function">row_number</code> () + → <code class="returnvalue">bigint</code> + </p> + <p> + Returns the number of the current row within its partition, counting + from 1. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.2.1.1.1" class="indexterm"></a> + <code class="function">rank</code> () + → <code class="returnvalue">bigint</code> + </p> + <p> + Returns the rank of the current row, with gaps; that is, + the <code class="function">row_number</code> of the first row in its peer + group. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.3.1.1.1" class="indexterm"></a> + <code class="function">dense_rank</code> () + → <code class="returnvalue">bigint</code> + </p> + <p> + Returns the rank of the current row, without gaps; this function + effectively counts peer groups. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.4.1.1.1" class="indexterm"></a> + <code class="function">percent_rank</code> () + → <code class="returnvalue">double precision</code> + </p> + <p> + Returns the relative rank of the current row, that is + (<code class="function">rank</code> - 1) / (total partition rows - 1). + The value thus ranges from 0 to 1 inclusive. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.5.1.1.1" class="indexterm"></a> + <code class="function">cume_dist</code> () + → <code class="returnvalue">double precision</code> + </p> + <p> + Returns the cumulative distribution, that is (number of partition rows + preceding or peers with current row) / (total partition rows). + The value thus ranges from 1/<em class="parameter"><code>N</code></em> to 1. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.6.1.1.1" class="indexterm"></a> + <code class="function">ntile</code> ( <em class="parameter"><code>num_buckets</code></em> <code class="type">integer</code> ) + → <code class="returnvalue">integer</code> + </p> + <p> + Returns an integer ranging from 1 to the argument value, dividing the + partition as equally as possible. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.7.1.1.1" class="indexterm"></a> + <code class="function">lag</code> ( <em class="parameter"><code>value</code></em> <code class="type">anyelement</code> + [<span class="optional">, <em class="parameter"><code>offset</code></em> <code class="type">integer</code> + [<span class="optional">, <em class="parameter"><code>default</code></em> <code class="type">anyelement</code> </span>]</span>] ) + → <code class="returnvalue">anyelement</code> + </p> + <p> + Returns <em class="parameter"><code>value</code></em> evaluated at + the row that is <em class="parameter"><code>offset</code></em> + rows before the current row within the partition; if there is no such + row, instead returns <em class="parameter"><code>default</code></em> + (which must be of the same type as + <em class="parameter"><code>value</code></em>). + Both <em class="parameter"><code>offset</code></em> and + <em class="parameter"><code>default</code></em> are evaluated + with respect to the current row. If omitted, + <em class="parameter"><code>offset</code></em> defaults to 1 and + <em class="parameter"><code>default</code></em> to <code class="literal">NULL</code>. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.8.1.1.1" class="indexterm"></a> + <code class="function">lead</code> ( <em class="parameter"><code>value</code></em> <code class="type">anyelement</code> + [<span class="optional">, <em class="parameter"><code>offset</code></em> <code class="type">integer</code> + [<span class="optional">, <em class="parameter"><code>default</code></em> <code class="type">anyelement</code> </span>]</span>] ) + → <code class="returnvalue">anyelement</code> + </p> + <p> + Returns <em class="parameter"><code>value</code></em> evaluated at + the row that is <em class="parameter"><code>offset</code></em> + rows after the current row within the partition; if there is no such + row, instead returns <em class="parameter"><code>default</code></em> + (which must be of the same type as + <em class="parameter"><code>value</code></em>). + Both <em class="parameter"><code>offset</code></em> and + <em class="parameter"><code>default</code></em> are evaluated + with respect to the current row. If omitted, + <em class="parameter"><code>offset</code></em> defaults to 1 and + <em class="parameter"><code>default</code></em> to <code class="literal">NULL</code>. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.9.1.1.1" class="indexterm"></a> + <code class="function">first_value</code> ( <em class="parameter"><code>value</code></em> <code class="type">anyelement</code> ) + → <code class="returnvalue">anyelement</code> + </p> + <p> + Returns <em class="parameter"><code>value</code></em> evaluated + at the row that is the first row of the window frame. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.10.1.1.1" class="indexterm"></a> + <code class="function">last_value</code> ( <em class="parameter"><code>value</code></em> <code class="type">anyelement</code> ) + → <code class="returnvalue">anyelement</code> + </p> + <p> + Returns <em class="parameter"><code>value</code></em> evaluated + at the row that is the last row of the window frame. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.5.8.28.6.2.2.11.1.1.1" class="indexterm"></a> + <code class="function">nth_value</code> ( <em class="parameter"><code>value</code></em> <code class="type">anyelement</code>, <em class="parameter"><code>n</code></em> <code class="type">integer</code> ) + → <code class="returnvalue">anyelement</code> + </p> + <p> + Returns <em class="parameter"><code>value</code></em> evaluated + at the row that is the <em class="parameter"><code>n</code></em>'th + row of the window frame (counting from 1); + returns <code class="literal">NULL</code> if there is no such row. + </p></td></tr></tbody></table></div></div><br class="table-break" /><p> + All of the functions listed in + <a class="xref" href="functions-window.html#FUNCTIONS-WINDOW-TABLE" title="Table 9.60. General-Purpose Window Functions">Table 9.60</a> depend on the sort ordering + specified by the <code class="literal">ORDER BY</code> clause of the associated window + definition. Rows that are not distinct when considering only the + <code class="literal">ORDER BY</code> columns are said to be <em class="firstterm">peers</em>. + The four ranking functions (including <code class="function">cume_dist</code>) are + defined so that they give the same answer for all rows of a peer group. + </p><p> + Note that <code class="function">first_value</code>, <code class="function">last_value</code>, and + <code class="function">nth_value</code> consider only the rows within the <span class="quote">“<span class="quote">window + frame</span>”</span>, which by default contains the rows from the start of the + partition through the last peer of the current row. This is + likely to give unhelpful results for <code class="function">last_value</code> and + sometimes also <code class="function">nth_value</code>. You can redefine the frame by + adding a suitable frame specification (<code class="literal">RANGE</code>, + <code class="literal">ROWS</code> or <code class="literal">GROUPS</code>) to + the <code class="literal">OVER</code> clause. + See <a class="xref" href="sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS" title="4.2.8. Window Function Calls">Section 4.2.8</a> for more information + about frame specifications. + </p><p> + When an aggregate function is used as a window function, it aggregates + over the rows within the current row's window frame. + An aggregate used with <code class="literal">ORDER BY</code> and the default window frame + definition produces a <span class="quote">“<span class="quote">running sum</span>”</span> type of behavior, which may or + may not be what's wanted. To obtain + aggregation over the whole partition, omit <code class="literal">ORDER BY</code> or use + <code class="literal">ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</code>. + Other frame specifications can be used to obtain other effects. + </p><div class="note"><h3 class="title">Note</h3><p> + The SQL standard defines a <code class="literal">RESPECT NULLS</code> or + <code class="literal">IGNORE NULLS</code> option for <code class="function">lead</code>, <code class="function">lag</code>, + <code class="function">first_value</code>, <code class="function">last_value</code>, and + <code class="function">nth_value</code>. This is not implemented in + <span class="productname">PostgreSQL</span>: the behavior is always the + same as the standard's default, namely <code class="literal">RESPECT NULLS</code>. + Likewise, the standard's <code class="literal">FROM FIRST</code> or <code class="literal">FROM LAST</code> + option for <code class="function">nth_value</code> is not implemented: only the + default <code class="literal">FROM FIRST</code> behavior is supported. (You can achieve + the result of <code class="literal">FROM LAST</code> by reversing the <code class="literal">ORDER BY</code> + ordering.) + </p></div></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-aggregate.html" title="9.21. Aggregate Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. 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