<literal>g</literal> flag which commands it to return all matches, not
     just the first one.
    </para>

   <para>
    Some examples:
<programlisting>
SELECT regexp_matches('foo', 'not there');
 regexp_matches
----------------
(0 rows)

SELECT regexp_matches('foobarbequebazilbarfbonk', '(b[^b]+)(b[^b]+)', 'g');
 regexp_matches
----------------
 {bar,beque}
 {bazil,barf}
(2 rows)
</programlisting>
   </para>

   <tip>
    <para>
     In most cases <function>regexp_matches()</function> should be used with
     the <literal>g</literal> flag, since if you only want the first match, it's
     easier and more efficient to use <function>regexp_match()</function>.
     However, <function>regexp_match()</function> only exists
     in <productname>PostgreSQL</productname> version 10 and up.  When working in older
     versions, a common trick is to place a <function>regexp_matches()</function>
     call in a sub-select, for example:
<programlisting>
SELECT col1, (SELECT regexp_matches(col2, '(bar)(beque)')) FROM tab;
</programlisting>
     This produces a text array if there's a match, or <literal>NULL</literal> if
     not, the same as <function>regexp_match()</function> would do.  Without the
     sub-select, this query would produce no output at all for table rows
     without a match, which is typically not the desired behavior.
    </para>
   </tip>

    <para>
     The <function>regexp_replace</function> function provides substitution of
     new text for substrings that match POSIX regular expression patterns.
     It has the syntax
     <function>regexp_replace</function>(<replaceable>string</replaceable>,
     <replaceable>pattern</replaceable>, <replaceable>replacement</replaceable>
     <optional>, <replaceable>flags</replaceable> </optional>)
     or
     <function>regexp_replace</function>(<replaceable>string</replaceable>,
     <replaceable>pattern</replaceable>, <replaceable>replacement</replaceable>,
     <replaceable>start</replaceable>
     <optional>, <replaceable>N</replaceable>
     <optional>, <replaceable>flags</replaceable> </optional></optional>).
     The source <replaceable>string</replaceable> is returned unchanged if
     there is no match to the <replaceable>pattern</replaceable>.  If there is a
     match, the <replaceable>string</replaceable> is returned with the
     <replaceable>replacement</replaceable> string substituted for the matching
     substring.  The <replaceable>replacement</replaceable> string can contain
     <literal>\</literal><replaceable>n</replaceable>, where <replaceable>n</replaceable> is 1
     through 9, to indicate that the source substring matching the
     <replaceable>n</replaceable>'th parenthesized subexpression of the pattern should be
     inserted, and it can contain <literal>\&amp;</literal> to indicate that the
     substring matching the entire pattern should be inserted.  Write
     <literal>\\</literal> if you need to put a literal backslash in the replacement
     text.
     <replaceable>pattern</replaceable> is searched for
     in <replaceable>string</replaceable>, normally from the beginning of
     the string, but if the <replaceable>start</replaceable> parameter is
     provided then beginning from that character index.
     By default, only the first match of the pattern is replaced.
     If <replaceable>N</replaceable> is specified and is greater than zero,
     then the <replaceable>N</replaceable>'th match of the pattern
     is replaced.
     If the <literal>g</literal> flag is given, or
     if <replaceable>N</replaceable> is specified and is zero, then all
     matches at or after the <replaceable>start</replaceable> position are
     replaced.  (The <literal>g</literal> flag is ignored
     when <replaceable>N</replaceable> is specified.)
     The <replaceable>flags</replaceable> parameter is an optional text
     string containing zero or more single-letter flags that change the
     function's behavior.  Supported flags (though
     not <literal>g</literal>)