How do I use regex in a SQLite query?

Question

As others pointed out already, REGEXP calls a user defined function which must first be defined and loaded into the the database. Maybe some sqlite distributions or GUI tools include it by default, but my Ubuntu install did not. The solution was

sudo apt-get install sqlite3-pcre

which implements Perl regular expressions in a loadable module in /usr/lib/sqlite3/pcre.so

To be able to use it, you have to load it each time you open the database:

.load /usr/lib/sqlite3/pcre.so

Or you could put that line into your ~/.sqliterc.

Now you can query like this:

SELECT fld FROM tbl WHERE fld REGEXP '\b3\b';

If you want to query directly from the command-line, you can use the -cmd switch to load the library before your SQL:

sqlite3 "$filename" -cmd ".load /usr/lib/sqlite3/pcre.so" "SELECT fld FROM tbl WHERE fld REGEXP '\b3\b';"

If you are on Windows, I guess a similar .dll file should be available somewhere.

SQLite3 supports the REGEXP operator:

WHERE x REGEXP <regex>

http://www.sqlite.org/lang_expr.html#regexp

A hacky way to solve it without regex is where ',' || x || ',' like '%,3,%'

SQLite does not contain regular expression functionality by default.

It defines a REGEXP operator, but this will fail with an error message unless you or your framework define a user function called regexp(). How you do this will depend on your platform.

If you have a regexp() function defined, you can match an arbitrary integer from a comma-separated list like so:

... WHERE your_column REGEXP "\b" || your_integer || "\b";

But really, it looks like you would find things a whole lot easier if you normalised your database structure by replacing those groups within a single column with a separate row for each number in the comma-separated list. Then you could not only use the = operator instead of a regular expression, but also use more powerful relational tools like joins that SQL provides for you.

A SQLite UDF in PHP/PDO for the REGEXP keyword that mimics the behavior in MySQL:

$pdo->sqliteCreateFunction('regexp',
    function ($pattern, $data, $delimiter = '~', $modifiers = 'isuS')
    {
        if (isset($pattern, $data) === true)
        {
            return (preg_match(sprintf('%1$s%2$s%1$s%3$s', $delimiter, $pattern, $modifiers), $data) > 0);
        }

        return null;
    }
);

The u modifier is not implemented in MySQL, but I find it useful to have it by default. Examples:

SELECT * FROM "table" WHERE "name" REGEXP 'sql(ite)*';
SELECT * FROM "table" WHERE regexp('sql(ite)*', "name", '#', 's');

If either $data or $pattern is NULL, the result is NULL - just like in MySQL.