MYSQL if a select query returns 0 rows then another select query?

Question

if select * from table where x=1 returns 0 rows, then I need select * from table where x=2 [or some other query]. Is it possible to do this in a si

Answer 1

If the two queries return different number of columns, you can pad one of the results with empty columns and also add an identifier column first.

SELECT SQL_CALC_FOUND_ROWS 1 query_type, mytable.*, 
'' col1, '' col2, '' col3, '' col4
FROM mytable
WHERE x = 1

UNION ALL

SELECT 2, mytable2.*
FROM mytable2
WHERE 
FOUND_ROWS() = 0 AND x = 2;

Where mytable2 has 4 more columns than mytable.