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create table t1 (a int primary key, b varchar(100) unique);
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insert into t1 values (2,"Beaker"),(3,"Cricket"), (1,"Shirty");
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EXPLAIN SELECT * FROM t1;
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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 2
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EXPLAIN SELECT a FROM t1 FORCE INDEX (PRIMARY) WHERE b="Beaker";
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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 2 Using where
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SELECT a FROM t1 FORCE INDEX (PRIMARY) WHERE b="Beaker";