I have query: SELECT DISTINCT a1, a2, a3 FROM t WHERE a4 = \'\' ORDER BY a1, a5
SELECT DISTINCT a1, a2, a3 FROM t WHERE a4 = \'\' ORDER BY a1, a5
and index: (a4, a1, a5, a2, a3)
(a4, a1, a5, a2, a3)
Query explain:
