REGEXP_REPLACE

Replaces the first match of a regular expression, or every match with the g flag.

Syntax

REGEXP_REPLACE( <string>, <pattern>, <replacement> [, <flags> ] )

Argument	Description
`<string>`	The text to change.
`<pattern>`	The regular expression to match. See the usage notes for the syntax.
`<replacement>`	The text to put in place of each match. `\1` to `\9` insert the pattern's groups, `\&` the whole match, and `\\` a backslash. A `$` is literal.
`<flags>`	Optional. `g` replaces every match, not just the first. `i` matches without case. Any other flag is an error.

Text. <string> unchanged when nothing matches. NULL when any argument is NULL.

Patterns use RE2 syntax, as in PostgreSQL for the common cases: classes like [0-9], \d, \s, \w, [[:alpha:]], anchors ^ and $, groups and alternation. RE2 has no lookahead, lookbehind or backreferences in the pattern; a pattern that uses them is an error.
The match is case sensitive unless the i flag is given.
On large tables the engine runs it in the data store when the pattern and replacement are literals, the call replaces every match (the g flag, or a pattern that starts with ^ and so can match only once), and the flags are g, i or both. The data store uses its own regular expression engine (Trino, Java style), so the engine also keeps a pattern in memory when it holds (?, \b, \B, \A, \z, \Z, \p, \P, \k, \Q, \E or a \ followed by a digit, and a replacement that holds $ or a backslash other than \1 to \9 and \&. With those rules both engines give the same result. Everything else runs after the rows are read, in RE2.

Keep only the digits:

SELECT c.key, REGEXP_REPLACE(c.phone, '[^0-9]', '', 'g') AS digits FROM Customer c

key	digits
C-104	61290001234

Reorder with groups:

SELECT i.number, REGEXP_REPLACE(i.issued, '^(\d{4})-(\d{2})-(\d{2})$', '\3/\2/\1') AS issued_au FROM data.invoices i

number	issued_au
412	15/03/2026

Only the first match, without the g flag:

SELECT REGEXP_REPLACE(f.name, '[ _]+', '-') AS slug FROM tables.drive.file f

slug
annual-report_final.pdf