How to order by in union all query.

Simple union all

SELECT id, name FROM table_a
UNION ALL
SELECT id, name FROM table_b

Wrong Case

SELECT id, name FROM table_a ORDER BY name DESC
UNION ALL
SELECT id, name FROM table_b ORDER BY name DESC

Correct Case

SELECT id, name FROM table_a
UNION ALL
SELECT id, name FROM table_b
ORDER BY name DESC