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306371a850
- added join cache indication in EXPLAIN (Extra column). - prefer filesort over full scan over index for ORDER BY (because it's faster). - when switching from REF to RANGE because RANGE uses longer key turn off sort on the head table only as the resulting RANGE access is a candidate for join cache and we don't want to disable it by sorting on the first table only.
52 lines
826 B
Text
52 lines
826 B
Text
drop table if exists t1;
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CREATE TABLE t1 (
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a char(5) NOT NULL,
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b char(4) NOT NULL,
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KEY (a),
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KEY (b)
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);
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INSERT INTO t1 VALUES ('A','B'),('b','A'),('C','c'),('D','E'),('a','a');
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select * from t1,t1 as t2;
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a b a b
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A B A B
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b A A B
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C c A B
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D E A B
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a a A B
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A B b A
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b A b A
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C c b A
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D E b A
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a a b A
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A B C c
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b A C c
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C c C c
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D E C c
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a a C c
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A B D E
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b A D E
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C c D E
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D E D E
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a a D E
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A B a a
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b A a a
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C c a a
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D E a a
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a a a a
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explain select t1.*,t2.* from t1,t1 as t2 where t1.A=t2.B;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ALL a NULL NULL NULL 5 Using join cache
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1 SIMPLE t2 ALL b NULL NULL NULL 5 Using where
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select t1.*,t2.* from t1,t1 as t2 where t1.A=t2.B order by binary t1.a,t2.a;
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a b a b
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A B a a
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A B b A
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C c C c
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a a a a
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a a b A
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b A A B
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select * from t1 where a='a';
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a b
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A B
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a a
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drop table t1;
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