Regular expressions are probably the most powerful text processing tool without programming.

SQLite does not support regular expressions by default. But you can easily enable them using the regexp extension.

Note. Unlike other DBMS, adding extensions in SQLite is a breeze. Download a file, run one database command — and you are good to go.

With regexp, matching a string against a pattern becomes as easy as:

-- count messages containing digits
select count(*) from messages
where msg_text regexp '\d+';
-- 42

Pattern matching and text replacement

There are three main tasks people usually solve using regular expressions:

1. Match a string against the pattern.
2. Extract a part of the string that matches the pattern.
3. Replace all parts of the string that match the pattern.

regexp provides a separate function for each of these tasks.

regexp_like(source, pattern)

Checks if the source string matches the pattern.

select regexp_like('Meet me at 10:30', '\d+:\d+');
-- 1
select regexp_like('Meet me at the cinema', '\d+:\d+');
-- 0

regexp_substr(source, pattern)

Returns a substring of the source string that matches the pattern.

select regexp_substr('Meet me at 10:30', '\d+:\d+');
-- 10:30

select regexp_substr('Meet me at 17:05', '\d+:\d+');
-- 17:05

regexp_replace(source, pattern, replacement)

Replaces all matching substrings with the replacement string.

select regexp_replace('password = "123456"', '"[^"]+"', '***');
-- password = ***

select regexp_replace('1 2 3 4', '[2468]', 'even');
-- 1 even 3 even

Pattern syntax

regexp supports pretty advanced syntax, including various groups, lazy quantifiers, and look-arounds:

select regexp_substr('the year is 2020', '(\d{2})\1');
-- 2020
select regexp_substr('the year is 2021', '(\d{2})\1');
-- (null)

select regexp_substr('1 2 3 2 4 5', '.*2');
-- 1 2 3 2
select regexp_substr('1 2 3 2 4 5', '.*?2');
-- 1 2

select regexp_substr('new year', '(\w+)\s(?=year)');
-- new
select regexp_substr('last year', '(\w+)\s(?=year)');
-- last

And much more! See documentation for details.