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Commit4f02cbc

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Doc: add cross-references between array_to_string and string_to_array.
These functions aren't exact inverses, but they're closely related;yet we document them in two different sections. Add cross-ref<link>s to improve that situation.While here, move the strpos and substr entries to re-alphabetizeTable 9.10. Also, drop an ancient compatibility note aboutstring_to_array, which wasn't even on the right page, so probablyfew people ever saw it.Discussion:https://postgr.es/m/164287017550.704.5840412183184961677@wrigleys.postgresql.org
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‎doc/src/sgml/func.sgml

Lines changed: 52 additions & 62 deletions
Original file line numberDiff line numberDiff line change
@@ -3508,54 +3508,6 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</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>strpos</primary>
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</indexterm>
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<function>strpos</function> ( <parameter>string</parameter> <type>text</type>, <parameter>substring</parameter> <type>text</type> )
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns first starting index of the specified <parameter>substring</parameter>
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within <parameter>string</parameter>, or zero if it's not present.
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(Same as <literal>position(<parameter>substring</parameter> in
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<parameter>string</parameter>)</literal>, but note the reversed
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argument order.)
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</para>
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<para>
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<literal>strpos('high', 'ig')</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>substr</primary>
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</indexterm>
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<function>substr</function> ( <parameter>string</parameter> <type>text</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
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<returnvalue>text</returnvalue>
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</para>
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<para>
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Extracts the substring of <parameter>string</parameter> starting at
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the <parameter>start</parameter>'th character,
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and extending for <parameter>count</parameter> characters if that is
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specified. (Same
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as <literal>substring(<parameter>string</parameter>
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from <parameter>start</parameter>
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for <parameter>count</parameter>)</literal>.)
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</para>
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<para>
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<literal>substr('alphabet', 3)</literal>
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<returnvalue>phabet</returnvalue>
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</para>
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<para>
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<literal>substr('alphabet', 3, 2)</literal>
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<returnvalue>ph</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>
@@ -3576,7 +3528,7 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
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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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<indexterm id="function-string-to-array">
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<primary>string_to_array</primary>
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</indexterm>
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<function>string_to_array</function> ( <parameter>string</parameter> <type>text</type>, <parameter>delimiter</parameter> <type>text</type> <optional>, <parameter>null_string</parameter> <type>text</type> </optional> )
@@ -3594,6 +3546,7 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
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If <parameter>null_string</parameter> is supplied and is
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not <literal>NULL</literal>, fields matching that string are
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replaced by <literal>NULL</literal>.
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See also <link linkend="function-array-to-string"><function>array_to_string</function></link>.
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</para>
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<para>
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<literal>string_to_array('xx~~yy~~zz', '~~', 'yy')</literal>
@@ -3633,6 +3586,54 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</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>strpos</primary>
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</indexterm>
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<function>strpos</function> ( <parameter>string</parameter> <type>text</type>, <parameter>substring</parameter> <type>text</type> )
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns first starting index of the specified <parameter>substring</parameter>
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within <parameter>string</parameter>, or zero if it's not present.
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(Same as <literal>position(<parameter>substring</parameter> in
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<parameter>string</parameter>)</literal>, but note the reversed
3602+
argument order.)
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</para>
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<para>
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<literal>strpos('high', 'ig')</literal>
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<returnvalue>2</returnvalue>
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</para></entry>
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</row>
3609+
3610+
<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>substr</primary>
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</indexterm>
3615+
<function>substr</function> ( <parameter>string</parameter> <type>text</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
3616+
<returnvalue>text</returnvalue>
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</para>
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<para>
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Extracts the substring of <parameter>string</parameter> starting at
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the <parameter>start</parameter>'th character,
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and extending for <parameter>count</parameter> characters if that is
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specified. (Same
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as <literal>substring(<parameter>string</parameter>
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from <parameter>start</parameter>
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for <parameter>count</parameter>)</literal>.)
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</para>
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<para>
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<literal>substr('alphabet', 3)</literal>
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<returnvalue>phabet</returnvalue>
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</para>
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<para>
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<literal>substr('alphabet', 3, 2)</literal>
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<returnvalue>ph</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>
@@ -18452,7 +18453,7 @@ SELECT NULLIF(value, '(none)') ...
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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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<indexterm id="function-array-to-string">
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<primary>array_to_string</primary>
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</indexterm>
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<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> )
@@ -18465,6 +18466,7 @@ SELECT NULLIF(value, '(none)') ...
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If <parameter>null_string</parameter> is given and is
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not <literal>NULL</literal>, then <literal>NULL</literal> array
1846718468
entries are represented by that string; otherwise, they are omitted.
18469+
See also <link linkend="function-string-to-array"><function>string_to_array</function></link>.
1846818470
</para>
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<para>
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<literal>array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')</literal>
@@ -18584,18 +18586,6 @@ SELECT NULLIF(value, '(none)') ...
1858418586
</tgroup>
1858518587
</table>
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18587-
<note>
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<para>
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There are two differences in the behavior of <function>string_to_array</function>
18590-
from pre-9.1 versions of <productname>PostgreSQL</productname>.
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First, it will return an empty (zero-element) array rather
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than <literal>NULL</literal> when the input string is of zero length.
18593-
Second, if the delimiter string is <literal>NULL</literal>, the function
18594-
splits the input into individual characters, rather than
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returning <literal>NULL</literal> as before.
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</para>
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</note>
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<para>
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See also <xref linkend="functions-aggregate"/> about the aggregate
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function <function>array_agg</function> for use with arrays.

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