MySQL Cast NULL to integer 0

Question

How can I cast something that returns NULL to 0?

If this is my query: select col from table; would this be the right way to do it: select cast(col as unsigned integer) from table;?

Thank you.

Answer 1

You'd probably want to use the COALESCE() function:

SELECT COALESCE(col, 0) FROM `table`; 

COALESCE() returns the first non-NULL value in the list, or NULL if there are no non-NULL values.

Test case:

CREATE TABLE `table` (id int, col int);  INSERT INTO `table` VALUES (1, 100); INSERT INTO `table` VALUES (2, NULL); INSERT INTO `table` VALUES (3, 300); INSERT INTO `table` VALUES (4, NULL); 

Result:

+------------------+ | COALESCE(col, 0) | +------------------+ |              100 | |                0 | |              300 | |                0 | +------------------+ 4 rows in set (0.00 sec) 

Answer 2

You can also use the IFNULL() function:

SELECT IFNULL(col, 0) FROM `table`; 

IFNULL(expr1, expr2) returns the first expression if it's not null, else returns the second expression.

Test case:

CREATE TABLE `table` (id int, col int);  INSERT INTO `table` VALUES (1, 100); INSERT INTO `table` VALUES (2, NULL); INSERT INTO `table` VALUES (3, 300); INSERT INTO `table` VALUES (4, NULL); 

Result:

+----------------+ | IFNULL(col, 0) | +----------------+ |            100 | |              0 | |            300 | |              0 | +----------------+ 4 rows in set (0.00 sec)