Typecast string to integer

Question

Wild guess: If your value is an empty string, you can use NULLIF to replace it for a NULL:

SELECT
    NULLIF(your_value, '')::int

You can even go one further and restrict on this coalesced field such as, for example:-

SELECT CAST(coalesce(<column>, '0') AS integer) as new_field
from <table>
where CAST(coalesce(<column>, '0') AS integer) >= 10; 

If you need to treat empty columns as NULLs, try this:

SELECT CAST(nullif(<column>, '') AS integer);

On the other hand, if you do have NULL values that you need to avoid, try:

SELECT CAST(coalesce(<column>, '0') AS integer);

I do agree, error message would help a lot.

The only way I succeed to not having an error because of NULL, or special characters or empty string is by doing this:

SELECT REGEXP_REPLACE(COALESCE(<column>::character varying, '0'), '[^0-9]*' ,'0')::integer FROM table

I'm not able to comment (too little reputation? I'm pretty new) on Lukas' post.

On my PG setup to_number(NULL) does not work, so my solution would be:

SELECT CASE WHEN column = NULL THEN NULL ELSE column :: Integer END
FROM table

If the value contains non-numeric characters, you can convert the value to an integer as follows:

SELECT CASE WHEN <column>~E'^\\d+$' THEN CAST (<column> AS INTEGER) ELSE 0 END FROM table;

The CASE operator checks the < column>, if it matches the integer pattern, it converts the rate into an integer, otherwise it returns 0

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: ""

Problem

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