Replace null with 0 in MySQL

Yes, by using COALESCE.

SELECT COALESCE(null_column, 0) AS null_column FROM whatever;

COALESCE goes through the list of values you give it, and returns the first non-null value.

I am adding this answer because no one mentioned IFNULL function

You can use IFNULL

SELECT IFNULL(column_name, 0) FROM table_name;

IFNULL will return column's value (if it has something other than NULL) otherwise second parameter passed (in this case 0).

There is the COALESCE method which return the first non-null parameter, in your case :

COALESCE(field, 0)

But you can use this if you want more :

COALESCE(field1, field2, 0)

If you messed up and have NULLs in existing table layout and want zeros, here is solution:

UPDATE `table` SET `somefield`=0 WHERE `somefield` is null

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