t-sql coalesce problem with space in column value
I have a SQL select statement using coalesce as following
SELECT COALESCE (A.FIRST_NAME, B.FIRST_NAME) AS FIRST_NAME,
COALESCE (A.LAST_NAME, B.LAST_NAME) AS LAST_NAME
FROM TEST_A A
INNER JOIN TEST_B B
ON A.ID = B.ID
It works as long as the A table column if is null, it shows the b table data.
My problem is table A has value of '' (space, not null value).
What can I do to fix this?