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func.sgml has grown over the years to the point where it is very difficult to manage. This commit splits out each sect1 piece into its own file, which is then included in the main file, so that the built documentation should be identical to the pre-split documentation. All these new files are placed in a new "func" subdirectory, and the previous func.sgml is removed. Done using scripts developed by: Author: jian he <jian.universality@gmail.com> Discussion: https://postgr.es/m/CACJufxFgAh1--EMwOjMuANe=VTmjkNaZjH+AzSe04-8ZCGiESA@mail.gmail.com
647 lines
23 KiB
Plaintext
647 lines
23 KiB
Plaintext
<sect1 id="functions-array">
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<title>Array Functions and Operators</title>
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<para>
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<xref linkend="array-operators-table"/> shows the specialized operators
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available for array types.
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In addition to those, the usual comparison operators shown in <xref
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linkend="functions-comparison-op-table"/> are available for
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arrays. The comparison operators compare the array contents
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element-by-element, using the default B-tree comparison function for
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the element data type, and sort based on the first difference.
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In multidimensional arrays the elements are visited in row-major order
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(last subscript varies most rapidly).
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If the contents of two arrays are equal but the dimensionality is
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different, the first difference in the dimensionality information
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determines the sort order.
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</para>
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<table id="array-operators-table">
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<title>Array Operators</title>
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<tgroup cols="1">
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<thead>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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Operator
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</para>
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<para>
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Description
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</para>
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<para>
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Example(s)
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</para></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<type>anyarray</type> <literal>@></literal> <type>anyarray</type>
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<returnvalue>boolean</returnvalue>
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</para>
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<para>
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Does the first array contain the second, that is, does each element
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appearing in the second array equal some element of the first array?
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(Duplicates are not treated specially,
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thus <literal>ARRAY[1]</literal> and <literal>ARRAY[1,1]</literal> are
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each considered to contain the other.)
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</para>
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<para>
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<literal>ARRAY[1,4,3] @> ARRAY[3,1,3]</literal>
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<returnvalue>t</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<type>anyarray</type> <literal><@</literal> <type>anyarray</type>
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<returnvalue>boolean</returnvalue>
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</para>
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<para>
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Is the first array contained by the second?
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</para>
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<para>
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<literal>ARRAY[2,2,7] <@ ARRAY[1,7,4,2,6]</literal>
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<returnvalue>t</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<type>anyarray</type> <literal>&&</literal> <type>anyarray</type>
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<returnvalue>boolean</returnvalue>
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</para>
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<para>
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Do the arrays overlap, that is, have any elements in common?
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</para>
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<para>
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<literal>ARRAY[1,4,3] && ARRAY[2,1]</literal>
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<returnvalue>t</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<type>anycompatiblearray</type> <literal>||</literal> <type>anycompatiblearray</type>
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Concatenates the two arrays. Concatenating a null or empty array is a
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no-op; otherwise the arrays must have the same number of dimensions
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(as illustrated by the first example) or differ in number of
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dimensions by one (as illustrated by the second).
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If the arrays are not of identical element types, they will be coerced
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to a common type (see <xref linkend="typeconv-union-case"/>).
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</para>
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<para>
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<literal>ARRAY[1,2,3] || ARRAY[4,5,6,7]</literal>
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<returnvalue>{1,2,3,4,5,6,7}</returnvalue>
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</para>
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<para>
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<literal>ARRAY[1,2,3] || ARRAY[[4,5,6],[7,8,9.9]]</literal>
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<returnvalue>{{1,2,3},{4,5,6},{7,8,9.9}}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<type>anycompatible</type> <literal>||</literal> <type>anycompatiblearray</type>
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Concatenates an element onto the front of an array (which must be
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empty or one-dimensional).
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</para>
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<para>
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<literal>3 || ARRAY[4,5,6]</literal>
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<returnvalue>{3,4,5,6}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<type>anycompatiblearray</type> <literal>||</literal> <type>anycompatible</type>
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Concatenates an element onto the end of an array (which must be
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empty or one-dimensional).
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</para>
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<para>
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<literal>ARRAY[4,5,6] || 7</literal>
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<returnvalue>{4,5,6,7}</returnvalue>
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</para></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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See <xref linkend="arrays"/> for more details about array operator
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behavior. See <xref linkend="indexes-types"/> for more details about
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which operators support indexed operations.
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</para>
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<para>
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<xref linkend="array-functions-table"/> shows the functions
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available for use with array types. See <xref linkend="arrays"/>
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for more information and examples of the use of these functions.
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</para>
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<table id="array-functions-table">
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<title>Array Functions</title>
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<tgroup cols="1">
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<thead>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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Function
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</para>
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<para>
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Description
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</para>
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<para>
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Example(s)
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</para></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_append</primary>
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</indexterm>
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<function>array_append</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> )
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Appends an element to the end of an array (same as
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the <type>anycompatiblearray</type> <literal>||</literal> <type>anycompatible</type>
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operator).
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</para>
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<para>
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<literal>array_append(ARRAY[1,2], 3)</literal>
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<returnvalue>{1,2,3}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_cat</primary>
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</indexterm>
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<function>array_cat</function> ( <type>anycompatiblearray</type>, <type>anycompatiblearray</type> )
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Concatenates two arrays (same as
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the <type>anycompatiblearray</type> <literal>||</literal> <type>anycompatiblearray</type>
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operator).
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</para>
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<para>
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<literal>array_cat(ARRAY[1,2,3], ARRAY[4,5])</literal>
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<returnvalue>{1,2,3,4,5}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_dims</primary>
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</indexterm>
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<function>array_dims</function> ( <type>anyarray</type> )
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<returnvalue>text</returnvalue>
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</para>
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<para>
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Returns a text representation of the array's dimensions.
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</para>
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<para>
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<literal>array_dims(ARRAY[[1,2,3], [4,5,6]])</literal>
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<returnvalue>[1:2][1:3]</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_fill</primary>
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</indexterm>
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<function>array_fill</function> ( <type>anyelement</type>, <type>integer[]</type>
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<optional>, <type>integer[]</type> </optional> )
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<returnvalue>anyarray</returnvalue>
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</para>
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<para>
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Returns an array filled with copies of the given value, having
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dimensions of the lengths specified by the second argument.
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The optional third argument supplies lower-bound values for each
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dimension (which default to all <literal>1</literal>).
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</para>
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<para>
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<literal>array_fill(11, ARRAY[2,3])</literal>
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<returnvalue>{{11,11,11},{11,11,11}}</returnvalue>
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</para>
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<para>
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<literal>array_fill(7, ARRAY[3], ARRAY[2])</literal>
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<returnvalue>[2:4]={7,7,7}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_length</primary>
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</indexterm>
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<function>array_length</function> ( <type>anyarray</type>, <type>integer</type> )
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns the length of the requested array dimension.
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(Produces NULL instead of 0 for empty or missing array dimensions.)
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</para>
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<para>
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<literal>array_length(array[1,2,3], 1)</literal>
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<returnvalue>3</returnvalue>
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</para>
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<para>
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<literal>array_length(array[]::int[], 1)</literal>
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<returnvalue>NULL</returnvalue>
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</para>
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<para>
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<literal>array_length(array['text'], 2)</literal>
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<returnvalue>NULL</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_lower</primary>
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</indexterm>
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<function>array_lower</function> ( <type>anyarray</type>, <type>integer</type> )
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns the lower bound of the requested array dimension.
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</para>
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<para>
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<literal>array_lower('[0:2]={1,2,3}'::integer[], 1)</literal>
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<returnvalue>0</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_ndims</primary>
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</indexterm>
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<function>array_ndims</function> ( <type>anyarray</type> )
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns the number of dimensions of the array.
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</para>
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<para>
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<literal>array_ndims(ARRAY[[1,2,3], [4,5,6]])</literal>
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<returnvalue>2</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_position</primary>
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</indexterm>
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<function>array_position</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> <optional>, <type>integer</type> </optional> )
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns the subscript of the first occurrence of the second argument
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in the array, or <literal>NULL</literal> if it's not present.
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If the third argument is given, the search begins at that subscript.
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The array must be one-dimensional.
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Comparisons are done using <literal>IS NOT DISTINCT FROM</literal>
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semantics, so it is possible to search for <literal>NULL</literal>.
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</para>
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<para>
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<literal>array_position(ARRAY['sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat'], 'mon')</literal>
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<returnvalue>2</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_positions</primary>
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</indexterm>
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<function>array_positions</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> )
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<returnvalue>integer[]</returnvalue>
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</para>
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<para>
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Returns an array of the subscripts of all occurrences of the second
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argument in the array given as first argument.
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The array must be one-dimensional.
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Comparisons are done using <literal>IS NOT DISTINCT FROM</literal>
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semantics, so it is possible to search for <literal>NULL</literal>.
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<literal>NULL</literal> is returned only if the array
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is <literal>NULL</literal>; if the value is not found in the array, an
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empty array is returned.
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</para>
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<para>
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<literal>array_positions(ARRAY['A','A','B','A'], 'A')</literal>
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<returnvalue>{1,2,4}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_prepend</primary>
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</indexterm>
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<function>array_prepend</function> ( <type>anycompatible</type>, <type>anycompatiblearray</type> )
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Prepends an element to the beginning of an array (same as
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the <type>anycompatible</type> <literal>||</literal> <type>anycompatiblearray</type>
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operator).
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</para>
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<para>
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<literal>array_prepend(1, ARRAY[2,3])</literal>
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<returnvalue>{1,2,3}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_remove</primary>
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</indexterm>
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<function>array_remove</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> )
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Removes all elements equal to the given value from the array.
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The array must be one-dimensional.
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Comparisons are done using <literal>IS NOT DISTINCT FROM</literal>
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semantics, so it is possible to remove <literal>NULL</literal>s.
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</para>
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<para>
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<literal>array_remove(ARRAY[1,2,3,2], 2)</literal>
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<returnvalue>{1,3}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_replace</primary>
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</indexterm>
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<function>array_replace</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type>, <type>anycompatible</type> )
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<returnvalue>anycompatiblearray</returnvalue>
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</para>
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<para>
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Replaces each array element equal to the second argument with the
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third argument.
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</para>
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<para>
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<literal>array_replace(ARRAY[1,2,5,4], 5, 3)</literal>
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<returnvalue>{1,2,3,4}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_reverse</primary>
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</indexterm>
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<function>array_reverse</function> ( <type>anyarray</type> )
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<returnvalue>anyarray</returnvalue>
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</para>
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<para>
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Reverses the first dimension of the array.
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</para>
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<para>
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<literal>array_reverse(ARRAY[[1,2],[3,4],[5,6]])</literal>
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<returnvalue>{{5,6},{3,4},{1,2}}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_sample</primary>
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</indexterm>
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<function>array_sample</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>n</parameter> <type>integer</type> )
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<returnvalue>anyarray</returnvalue>
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</para>
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<para>
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Returns an array of <parameter>n</parameter> items randomly selected
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from <parameter>array</parameter>. <parameter>n</parameter> may not
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exceed the length of <parameter>array</parameter>'s first dimension.
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If <parameter>array</parameter> is multi-dimensional,
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an <quote>item</quote> is a slice having a given first subscript.
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</para>
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<para>
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<literal>array_sample(ARRAY[1,2,3,4,5,6], 3)</literal>
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<returnvalue>{2,6,1}</returnvalue>
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</para>
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<para>
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<literal>array_sample(ARRAY[[1,2],[3,4],[5,6]], 2)</literal>
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<returnvalue>{{5,6},{1,2}}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_shuffle</primary>
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</indexterm>
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<function>array_shuffle</function> ( <type>anyarray</type> )
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<returnvalue>anyarray</returnvalue>
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</para>
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<para>
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Randomly shuffles the first dimension of the array.
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</para>
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<para>
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<literal>array_shuffle(ARRAY[[1,2],[3,4],[5,6]])</literal>
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<returnvalue>{{5,6},{1,2},{3,4}}</returnvalue>
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>array_sort</primary>
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</indexterm>
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<function>array_sort</function> (
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<parameter>array</parameter> <type>anyarray</type>
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<optional>, <parameter>descending</parameter> <type>boolean</type>
|
|
<optional>, <parameter>nulls_first</parameter> <type>boolean</type>
|
|
</optional></optional> )
|
|
<returnvalue>anyarray</returnvalue>
|
|
</para>
|
|
<para>
|
|
Sorts the first dimension of the array.
|
|
The sort order is determined by the default sort ordering of the
|
|
array's element type; however, if the element type is collatable,
|
|
the collation to use can be specified by adding
|
|
a <literal>COLLATE</literal> clause to
|
|
the <parameter>array</parameter> argument.
|
|
</para>
|
|
<para>
|
|
If <parameter>descending</parameter> is true then sort in
|
|
descending order, otherwise ascending order. If omitted, the
|
|
default is ascending order.
|
|
If <parameter>nulls_first</parameter> is true then nulls appear
|
|
before non-null values, otherwise nulls appear after non-null
|
|
values.
|
|
If omitted, <parameter>nulls_first</parameter> is taken to have
|
|
the same value as <parameter>descending</parameter>.
|
|
</para>
|
|
<para>
|
|
<literal>array_sort(ARRAY[[2,4],[2,1],[6,5]])</literal>
|
|
<returnvalue>{{2,1},{2,4},{6,5}}</returnvalue>
|
|
</para></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry role="func_table_entry"><para role="func_signature">
|
|
<indexterm id="function-array-to-string">
|
|
<primary>array_to_string</primary>
|
|
</indexterm>
|
|
<function>array_to_string</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>delimiter</parameter> <type>text</type> <optional>, <parameter>null_string</parameter> <type>text</type> </optional> )
|
|
<returnvalue>text</returnvalue>
|
|
</para>
|
|
<para>
|
|
Converts each array element to its text representation, and
|
|
concatenates those separated by
|
|
the <parameter>delimiter</parameter> string.
|
|
If <parameter>null_string</parameter> is given and is
|
|
not <literal>NULL</literal>, then <literal>NULL</literal> array
|
|
entries are represented by that string; otherwise, they are omitted.
|
|
See also <link linkend="function-string-to-array"><function>string_to_array</function></link>.
|
|
</para>
|
|
<para>
|
|
<literal>array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')</literal>
|
|
<returnvalue>1,2,3,*,5</returnvalue>
|
|
</para></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry role="func_table_entry"><para role="func_signature">
|
|
<indexterm>
|
|
<primary>array_upper</primary>
|
|
</indexterm>
|
|
<function>array_upper</function> ( <type>anyarray</type>, <type>integer</type> )
|
|
<returnvalue>integer</returnvalue>
|
|
</para>
|
|
<para>
|
|
Returns the upper bound of the requested array dimension.
|
|
</para>
|
|
<para>
|
|
<literal>array_upper(ARRAY[1,8,3,7], 1)</literal>
|
|
<returnvalue>4</returnvalue>
|
|
</para></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry role="func_table_entry"><para role="func_signature">
|
|
<indexterm>
|
|
<primary>cardinality</primary>
|
|
</indexterm>
|
|
<function>cardinality</function> ( <type>anyarray</type> )
|
|
<returnvalue>integer</returnvalue>
|
|
</para>
|
|
<para>
|
|
Returns the total number of elements in the array, or 0 if the array
|
|
is empty.
|
|
</para>
|
|
<para>
|
|
<literal>cardinality(ARRAY[[1,2],[3,4]])</literal>
|
|
<returnvalue>4</returnvalue>
|
|
</para></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry role="func_table_entry"><para role="func_signature">
|
|
<indexterm>
|
|
<primary>trim_array</primary>
|
|
</indexterm>
|
|
<function>trim_array</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>n</parameter> <type>integer</type> )
|
|
<returnvalue>anyarray</returnvalue>
|
|
</para>
|
|
<para>
|
|
Trims an array by removing the last <parameter>n</parameter> elements.
|
|
If the array is multidimensional, only the first dimension is trimmed.
|
|
</para>
|
|
<para>
|
|
<literal>trim_array(ARRAY[1,2,3,4,5,6], 2)</literal>
|
|
<returnvalue>{1,2,3,4}</returnvalue>
|
|
</para></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry role="func_table_entry"><para role="func_signature">
|
|
<indexterm>
|
|
<primary>unnest</primary>
|
|
</indexterm>
|
|
<function>unnest</function> ( <type>anyarray</type> )
|
|
<returnvalue>setof anyelement</returnvalue>
|
|
</para>
|
|
<para>
|
|
Expands an array into a set of rows.
|
|
The array's elements are read out in storage order.
|
|
</para>
|
|
<para>
|
|
<literal>unnest(ARRAY[1,2])</literal>
|
|
<returnvalue></returnvalue>
|
|
<programlisting>
|
|
1
|
|
2
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
<literal>unnest(ARRAY[['foo','bar'],['baz','quux']])</literal>
|
|
<returnvalue></returnvalue>
|
|
<programlisting>
|
|
foo
|
|
bar
|
|
baz
|
|
quux
|
|
</programlisting>
|
|
</para></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry role="func_table_entry"><para role="func_signature">
|
|
<function>unnest</function> ( <type>anyarray</type>, <type>anyarray</type> <optional>, ... </optional> )
|
|
<returnvalue>setof anyelement, anyelement [, ... ]</returnvalue>
|
|
</para>
|
|
<para>
|
|
Expands multiple arrays (possibly of different data types) into a set of
|
|
rows. If the arrays are not all the same length then the shorter ones
|
|
are padded with <literal>NULL</literal>s. This form is only allowed
|
|
in a query's FROM clause; see <xref linkend="queries-tablefunctions"/>.
|
|
</para>
|
|
<para>
|
|
<literal>select * from unnest(ARRAY[1,2], ARRAY['foo','bar','baz']) as x(a,b)</literal>
|
|
<returnvalue></returnvalue>
|
|
<programlisting>
|
|
a | b
|
|
---+-----
|
|
1 | foo
|
|
2 | bar
|
|
| baz
|
|
</programlisting>
|
|
</para></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>
|
|
See also <xref linkend="functions-aggregate"/> about the aggregate
|
|
function <function>array_agg</function> for use with arrays.
|
|
</para>
|
|
</sect1>
|