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46 lines
1.5 KiB
Text
46 lines
1.5 KiB
Text
drop table if exists t1;
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create table t1 (id int not null, str char(10), unique(str));
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explain select * from t1;
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table type possible_keys key key_len ref rows Extra
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t1 system NULL NULL NULL NULL 0 const row not found
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insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
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select * from t1 where str is null;
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id str
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1 NULL
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2 NULL
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select * from t1 where str="foo";
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id str
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3 foo
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explain select * from t1 where str is null;
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table type possible_keys key key_len ref rows Extra
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t1 ref str str 11 const 1 Using where
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explain select * from t1 where str="foo";
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table type possible_keys key key_len ref rows Extra
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t1 const str str 11 const 1
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explain select * from t1 ignore key (str) where str="foo";
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table type possible_keys key key_len ref rows Extra
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t1 ALL NULL NULL NULL NULL 4 Using where
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explain select * from t1 use key (str,str) where str="foo";
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table type possible_keys key key_len ref rows Extra
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t1 const str str 11 const 1
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explain select * from t1 use key (str,str,foo) where str="foo";
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Key column 'foo' doesn't exist in table
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explain select * from t1 ignore key (str,str,foo) where str="foo";
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Key column 'foo' doesn't exist in table
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drop table t1;
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explain select 1;
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Comment
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No tables used
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create table t1 (a int not null);
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explain select count(*) from t1;
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Comment
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Select tables optimized away
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insert into t1 values(1);
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explain select count(*) from t1;
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Comment
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Select tables optimized away
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insert into t1 values(1);
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explain select count(*) from t1;
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Comment
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Select tables optimized away
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drop table t1;
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