Common issue

Naively type casting any string into an integer like so

SELECT ''::integer

Often results to the famous error:

Query failed: ERROR: invalid input syntax for integer: ""

PostgreSQL has no pre-defined function for safely type casting any string into an integer.

Solution

Create a user-defined function inspired by PHP’s intval() function.

CREATE FUNCTION intval(character varying) RETURNS integer AS $$

SELECT
CASE
    WHEN length(btrim(regexp_replace($1, '[^0-9]', '','g')))>0 THEN btrim(regexp_replace($1, '[^0-9]', '','g'))::integer
    ELSE 0
END AS intval;

$$
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;

Usage

/* Example 1 */
SELECT intval('9000');
-- output: 9000

/* Example 2 */
SELECT intval('9gag');
-- output: 9

/* Example 3 */
SELECT intval('the quick brown fox jumps over the lazy dog');
-- output: 0