MySQL: select * from table where col IN (null, “”) possible without OR

Question

SELECT  *
FROM    mytable
WHERE   COALESCE(col, '') = ''

Note, however, than OR query will be much more efficient if the column is indexed:

SELECT  *
FROM    mytable
WHERE   col="" OR col IS NULL

This will use ref_or_null access path on the index.

If you need to select from a list of values along with NULLs, just put all not-null values into the list and add a single OR IS NULL condition:

SELECT  *
FROM    mytable
WHERE   col IN ('val1', 'val2', 'val3') OR col IS NULL

This will use an index on col as well.