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CREATE TABLE t1 (
a smallint,
b smallint,
c smallint,
KEY a (a),
KEY b (b)
) ENGINE = MyISAM
PARTITION BY HASH (c) PARTITIONS 3;
CREATE TABLE t2 (a tinyint) ENGINE = MyISAM;
INSERT INTO t2 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11),(12),(13),
(14),(15),(16);
SET SESSION optimizer_switch="index_merge=on";
SET SESSION optimizer_switch="index_merge_intersection=on";
SET SESSION optimizer_switch="index_merge_union=off";
SET SESSION optimizer_switch="index_merge_sort_union=off";
INSERT INTO t1 VALUES (1,1,0), (1,1,0), (2,1,0), (2,2,1), (1,1,1), (2,2,4);
# Add some rows to make the index_merge_intersect possible
INSERT INTO t1 SELECT 1,1,0 FROM t2 A, t2 B;
INSERT INTO t1 SELECT 1,1,1 FROM t2 A, t2 B;
INSERT INTO t1 SELECT 1,1,2 FROM t2 A, t2 B LIMIT 68;
SELECT COUNT(*) FROM t1;
COUNT(*)
586
ANALYZE TABLE t1;
Table Op Msg_type Msg_text
test.t1 analyze status OK
EXPLAIN SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge a,b b,a 3,3 NULL 1 Using intersect(b,a); Using where
# Before fix:
# (p0 - partition 0, R3 - 3rd record in that partition = offset)
# Make 'a' read p0-R3, p1-R1, p1-R3
# Make 'b' read p1-R1, p1-R3
# 'b' will skip p1-R1 since R3 is bigger than R1.
SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
a b c
2 2 1
2 2 4
SET @old_opt_switch = @@session.optimizer_switch;
SET SESSION optimizer_switch="index_merge_intersection=off";
# Without index_merge_intersection
SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
a b c
2 2 1
2 2 4
EXPLAIN SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a,b b 3 const 2 Using where
SET SESSION optimizer_switch="index_merge_union=on";
EXPLAIN SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge a,b b,a 3,3 NULL 5 Using union(b,a); Using where
SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
a b c
2 2 1
2 2 4
SET SESSION optimizer_switch="index_merge_union=off";
SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
a b c
2 2 1
2 2 4
EXPLAIN SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL a,b NULL NULL NULL 586 Using where
SET SESSION optimizer_switch="index_merge_sort_union=on";
EXPLAIN SELECT a,b,c FROM t1 WHERE (b >= 2 OR a >= 2) AND c > 0 AND c < 100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge a,b b,a 3,3 NULL 10 Using sort_union(b,a); Using where
# Not affected, added for completeness...
SELECT a,b,c FROM t1 WHERE (b >= 2 OR a >= 2) AND c > 0 AND c < 100;
a b c
2 2 1
2 2 4
SET SESSION optimizer_switch="index_merge_sort_union=off";
SELECT a,b,c FROM t1 WHERE (b >= 2 OR a >= 2) AND c > 0 AND c < 100;
a b c
2 2 1
2 2 4
EXPLAIN SELECT a,b,c FROM t1 WHERE (b >= 2 OR a >= 2) AND c > 0 AND c < 100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL a,b NULL NULL NULL 586 Using where
SET @@session.optimizer_switch = @old_opt_switch;
DROP TABLE t1, t2;
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