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# # Bug 20219846: EXPLAIN FOR LIMIT QUERY SHOWS FILESORT BUT EXECUTION # IS DONE WITH INDEX ONLY # CREATE TABLE t0 ( i0 INTEGER NOT NULL ); INSERT INTO t0 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9); CREATE TABLE t1 ( pk INTEGER PRIMARY KEY, i1 INTEGER NOT NULL, i2 INTEGER NOT NULL, INDEX k1 (i1) ) ENGINE=InnoDB; INSERT INTO t1 SELECT a0.i0 + 10*a1.i0 + 100*a2.i0, (a0.i0 + 10*a1.i0 + 100*a2.i0) % 50, a0.i0 + 10*a1.i0 + 100*a2.i0 FROM t0 AS a0, t0 AS a1, t0 AS a2; CREATE TABLE t2 ( pk INTEGER PRIMARY KEY, i1 INTEGER NOT NULL, i2 INTEGER NOT NULL, INDEX k1 (i1) ) ENGINE=InnoDB; INSERT INTO t2 SELECT a0.i0 + 10*a1.i0 + 100*a2.i0, (a0.i0 + 10*a1.i0 + 100*a2.i0) % 500, a0.i0 + 10*a1.i0 + 100*a2.i0 FROM t0 AS a0, t0 AS a1, t0 AS a2; ANALYZE TABLE t1,t2; Table Op Msg_type Msg_text test.t1 analyze status OK test.t2 analyze status OK # Explain should show "Using filesort" EXPLAIN SELECT * FROM t1 JOIN t2 ON t1.i1=t2.i1 WHERE t2.i2 > 3 ORDER BY t1.i1 LIMIT 20; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL k1 NULL NULL NULL 1000 100.00 Using filesort 1 SIMPLE t2 NULL ref k1 k1 4 test.t1.i1 2 33.33 Using where Warnings: Note 1003 /* select#1 */ select `test`.`t1`.`pk` AS `pk`,`test`.`t1`.`i1` AS `i1`,`test`.`t1`.`i2` AS `i2`,`test`.`t2`.`pk` AS `pk`,`test`.`t2`.`i1` AS `i1`,`test`.`t2`.`i2` AS `i2` from `test`.`t1` join `test`.`t2` where ((`test`.`t2`.`i1` = `test`.`t1`.`i1`) and (`test`.`t2`.`i2` > 3)) order by `test`.`t1`.`i1` limit 20 FLUSH STATUS; SELECT * FROM t1 JOIN t2 ON t1.i1=t2.i1 WHERE t2.i2 > 3 ORDER BY t1.i1 LIMIT 20; pk i1 i2 pk i1 i2 0 0 0 500 0 500 50 0 50 500 0 500 100 0 100 500 0 500 150 0 150 500 0 500 200 0 200 500 0 500 250 0 250 500 0 500 300 0 300 500 0 500 350 0 350 500 0 500 400 0 400 500 0 500 450 0 450 500 0 500 500 0 500 500 0 500 550 0 550 500 0 500 600 0 600 500 0 500 650 0 650 500 0 500 700 0 700 500 0 500 750 0 750 500 0 500 800 0 800 500 0 500 850 0 850 500 0 500 900 0 900 500 0 500 950 0 950 500 0 500 # Status from execution should show that filesort was used SHOW STATUS LIKE 'Sort%'; Variable_name Value Sort_merge_passes 0 Sort_range 0 Sort_rows 1000 Sort_scan 1 DROP TABLE t0, t1, t2;