How to use MySQL UNION in qa_db_query_sub function?

Question

Although it seems that qa_db_query_sub function will be deprecated in Q2A 1.9.0, but still I would like to ask how to use MySQL UNION in qa_db_query_sub function?

This simple SELECT function works well

SELECT postid FROM  `qa_posts`  WHERE `type`="Q"  ORDER  BY created DESC  LIMIT  1

qa_db_read_all_assoc(qa_db_query_sub('SELECT postid FROM  `qa_posts`  WHERE `type`="Q"  ORDER  BY created DESC  LIMIT  1'));

But this compound function doesn't work:

SELECT postid FROM  `qa_posts`  WHERE `type`="Q"  ORDER  BY created DESC  LIMIT  1 UNION ALL SELECT postid FROM  `another_posts`  WHERE `type`="Q"  ORDER  BY created DESC  LIMIT  1

Or even this doesn't work either

(SELECT postid FROM  `qa_posts`  WHERE `type`="Q"  ORDER  BY created DESC  LIMIT  1) UNION ALL (SELECT postid FROM  `another_posts`  WHERE `type`="Q"  ORDER  BY created DESC  LIMIT  1)

qa_posts and another_posts have the same structure in this example.

Comments

"Doesn't work" is not a valid problem description. What result did you expect? What result did you get? Your first UNION ALL query is syntactically incorrect, so it should cause an error. The second UNION ALL query is correct and should work. At least it did for me when I just tested it.

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Thank you very much.