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DROP TABLE IF EXISTS t1;
CREATE TABLE t1
(a INT AUTO_INCREMENT PRIMARY KEY,
b CHAR(20)
);
SET @start_value= @@global.max_seeks_for_key;
'#--------------------FN_DYNVARS_084_01-------------------------#'
SELECT @@global.max_seeks_for_key = 10;
@@global.max_seeks_for_key = 10
0
SELECT @@session.max_seeks_for_key = 10;
@@session.max_seeks_for_key = 10
0
SET @@global.max_seeks_for_key = 20;
SELECT @@global.max_seeks_for_key;
@@global.max_seeks_for_key
20
INSERT INTO t1(b) VALUES("AREc");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1
1 SIMPLE t2 system NULL NULL NULL NULL 1
SET @@session.max_seeks_for_key = 2;
SELECT @@session.max_seeks_for_key;
@@session.max_seeks_for_key
2
INSERT INTO t1(b) VALUES("BREc");
INSERT INTO t1(b) VALUES("CRec");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3
1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where; Using join buffer
'#--------------------FN_DYNVARS_084_02-------------------------#'
SELECT @@global.max_seeks_for_key = 10;
@@global.max_seeks_for_key = 10
0
SELECT @@session.max_seeks_for_key = 10;
@@session.max_seeks_for_key = 10
0
SET @@global.max_seeks_for_key = 20;
SELECT @@global.max_seeks_for_key;
@@global.max_seeks_for_key
20
INSERT INTO t1(b) VALUES("AREc");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4
1 SIMPLE t2 ALL NULL NULL NULL NULL 4 Using where; Using join buffer
SET @@session.max_seeks_for_key = 2;
SELECT @@session.max_seeks_for_key;
@@session.max_seeks_for_key
2
INSERT INTO t1(b) VALUES("BREc");
INSERT INTO t1(b) VALUES("CRec");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 6
1 SIMPLE t2 ALL NULL NULL NULL NULL 6 Using where; Using join buffer
INSERT INTO t1 VALUES(null,"test");
INSERT INTO t1 VALUES (null,"a"),(null,"a"),(null,"a"),
(null,"a"),(null,"a"),(null,"a"),(null,"a"),
(null,"a"),(null,"a"),(null,"a");
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 17
1 SIMPLE t2 ALL NULL NULL NULL NULL 17 Using where; Using join buffer
ANALYZE TABLE t1;
Table Op Msg_type Msg_text
test.t1 analyze status OK
SET MAX_SEEKS_FOR_KEY=1;
EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 17
1 SIMPLE t2 ALL NULL NULL NULL NULL 17 Using where; Using join buffer
SET MAX_SEEKS_FOR_KEY=DEFAULT;
DROP TABLE t1;
SET @@global.max_seeks_for_key= @start_value;
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