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22 lines
1 KiB
Text
22 lines
1 KiB
Text
drop table if exists t1, t2;
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create table t1 (a int);
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insert into t1 values (0),(1),(2),(3);
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create table t2 (a int primary key, b int)
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as select a, a as b from t1 where a in (1,2);
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explain select t1.a from t1 left join t2 on t2.a=t1.a;
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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 NULL NULL NULL NULL 4
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set optimizer_switch='table_elimination=off';
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explain select t1.a from t1 left join t2 on t2.a=t1.a;
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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 NULL NULL NULL NULL 4
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1 SIMPLE t2 eq_ref PRIMARY PRIMARY 4 test.t1.a 1 Using index
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set optimizer_switch='table_elimination=on';
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explain select t1.a from t1 left join t2 on t2.a=t1.a;
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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 NULL NULL NULL NULL 4
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set optimizer_switch='table_elimination=default';
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explain select t1.a from t1 left join t2 on t2.a=t1.a;
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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 NULL NULL NULL NULL 4
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drop table t1, t2;
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