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create table t1 (
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a VARCHAR(900),
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b int
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);
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insert into t1 values
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( 0 , 1 ),
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( 1 , 2 ),
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( 2 , 3 ),
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( 3 , 4 ),
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( 4 , 5 ),
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( 5 , 6 ),
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( 6 , 7 ),
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( 7 , 8 ),
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( 8 , 9 ),
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( 9 , 10 ),
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( 10 , 11 ),
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( 11 , 12 ),
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( 12 , 13 ),
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( 13 , 14 ),
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( 14 , 15 ),
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( 15 , 16 ),
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( 16 , 17 ),
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( 17 , 18 ),
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( 18 , 19 ),
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( 25 , 26 ),
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( 26 , 27 ),
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( 9 , 120 ),
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( 10 , 121 ),
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( 11 , 122 ),
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( 12 , 123 ),
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( 13 , 124 ),
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( 14 , 125 ),
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( 15 , 126 ),
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( 16 , 127 );
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select count(distinct a) from t1;
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count(distinct a)
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21
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set tmp_table_size=1024;
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select count(distinct a) from t1;
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count(distinct a)
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19
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So when we set the value of tmp_table_size=1024, then the result for the select query is incorrect
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