45bc789a0f
For the following two reason, we should not push stream agg down to double read - The aggregate will lost the handle information - There's no sort operator. The second read is ordered with pk, not by index.
42 lines
1.5 KiB
Plaintext
42 lines
1.5 KiB
Plaintext
drop table if exists t;
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create table t (id int, c1 timestamp);
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show columns from t;
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Field Type Null Key Default Extra
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id int(11) YES NULL
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c1 timestamp YES NULL
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explain t;
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Field Type Null Key Default Extra
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id int(11) YES NULL
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c1 timestamp YES NULL
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describe t;
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Field Type Null Key Default Extra
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id int(11) YES NULL
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c1 timestamp YES NULL
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desc t;
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Field Type Null Key Default Extra
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id int(11) YES NULL
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c1 timestamp YES NULL
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desc t c1;
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Field Type Null Key Default Extra
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c1 timestamp YES NULL
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desc t id;
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Field Type Null Key Default Extra
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id int(11) YES NULL
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drop table if exists t;
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create table t(id int primary key, a int, b int);
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set session tidb_hashagg_partial_concurrency = 1;
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set session tidb_hashagg_final_concurrency = 1;
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explain select group_concat(a) from t group by id;
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id count task operator info
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StreamAgg_8 8000.00 root group by:Column#7, funcs:group_concat(Column#6, ",")
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└─Projection_18 10000.00 root cast(Column#2), Column#1
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└─TableReader_15 10000.00 root data:TableScan_14
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└─TableScan_14 10000.00 cop[tikv] table:t, range:[-inf,+inf], keep order:true, stats:pseudo
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explain select group_concat(a, b) from t group by id;
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id count task operator info
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StreamAgg_8 8000.00 root group by:Column#8, funcs:group_concat(Column#6, Column#7, ",")
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└─Projection_18 10000.00 root cast(Column#2), cast(Column#3), Column#1
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└─TableReader_15 10000.00 root data:TableScan_14
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└─TableScan_14 10000.00 cop[tikv] table:t, range:[-inf,+inf], keep order:true, stats:pseudo
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drop table t;
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