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

SQL_CALC_FOUND_ROWS and FOUND_ROWS cannot be used in a single query, even if separate by UNION statements.

The correct way to do this would be:

WITH  my_cte AS
(
  SELECT * from original_set
)
SELECT * FROM my_cte
UNION ALL
SELECT opt.* FROM optional_set opt JOIN (SELECT count(*) v FROM my_cte) count ON count.v=0;

With the JOIN and the UNION ALL the performance of this query is almost equivalent to either of the individual standalone queries