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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);
--echo # 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;
ANALYZE TABLE t1;
# For plan debugging
let $use_optimizer_trace=0;
if ($use_optimizer_trace)
{
SET optimizer_trace="enabled=on";
}
EXPLAIN SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
if ($use_optimizer_trace)
{
SELECT TRACE FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
}
--echo # Before fix:
--echo # (p0 - partition 0, R3 - 3rd record in that partition = offset)
--echo # Make 'a' read p0-R3, p1-R1, p1-R3
--echo # Make 'b' read p1-R1, p1-R3
--echo # 'b' will skip p1-R1 since R3 is bigger than R1.
# b reads first row from p1 (0x0)
# b returns 0x0 from p1
# a reads 3rd row from p0 (0xe)
# a read first row from p1 (0x0)
# a returns 0xe from p0
# b skips (0xe from p0 > 0x0 from p1)
# b reads 3rd row from p1 (0xe)
# b returns 0xe from p1
# a skips (0xe from p1 > 0xe from p0)
# a returns 0x0 from p1
# a reads 3rd row from p1 (0xe)
# a returns 0xe from p1
# MATCH! (0xe from p1 == 0xe from p1)
SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
SET @old_opt_switch = @@session.optimizer_switch;
SET SESSION optimizer_switch="index_merge_intersection=off";
--echo # Without index_merge_intersection
SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
EXPLAIN SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2;
SET SESSION optimizer_switch="index_merge_union=on";
EXPLAIN SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
if ($use_optimizer_trace)
{
SELECT TRACE FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
}
# First there where a bug where index_init() was called with sorted=false :(
# Before fix of secondary sort in ha_partition:
# b reads first row from p1 (0x0)
# b returns 0x0 from p1
# a reads 3rd row from p0 (0xe)
# a read first row from p1 (0x0)
# a returns 0xe from p0
# b < a in priority queue
# b reads 3rd row from p1 (0xe)
# b returns 0xe from p1
# Fetch row 0x0 from p1 (2,2,1)
# a returns 0x0 frop p1
# Fetch row 0xe from p0 (2,1,0), but is filtered away from evaluate_join_record
# a reads 3rd from from p1 (0xe)
# a returns 0xe from p1
# Fetch row 0x0 from p1 (2,2,1) (Dup, doh).
# Fetch row 0xe from p1 (2,2,4)
SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
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;
EXPLAIN SELECT a,b,c FROM t1 WHERE (b = 2 OR a = 2) AND c > 0 AND c < 100;
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;
if ($use_optimizer_trace)
{
SELECT TRACE FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
SET SESSION optimizer_trace="enabled=off";
}
--echo # Not affected, added for completeness...
# Verified that it does not demand sorted results, index_init(sorted=false)!
SELECT a,b,c FROM t1 WHERE (b >= 2 OR a >= 2) AND c > 0 AND c < 100;
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;
EXPLAIN SELECT a,b,c FROM t1 WHERE (b >= 2 OR a >= 2) AND c > 0 AND c < 100;
SET @@session.optimizer_switch = @old_opt_switch;
DROP TABLE t1, t2;
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