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fix the operator info #15291

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Nov 9, 2023
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fix the operator info #15291

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bfa9c2c
fix the operator info
qiancai Nov 8, 2023
42c82cf
Update explain-subqueries.md
qiancai Nov 8, 2023
b453614
Update explain-subqueries.md
qiancai Nov 8, 2023
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2 changes: 1 addition & 1 deletion correlated-subquery-optimization.md
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Expand Up @@ -100,4 +100,4 @@ explain select * from t1 where t1.a < (select sum(t2.a) from t2 where t2.b = t1.
+------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+
```

After disabling the subquery decorrelation rule, you can see `range: decided by [eq(test.t2.b, test.t1.b)]` in `operator info` of `IndexRangeScan_25(Build)`. It means that the decorrelation of correlated subquery is not performed and TiDB uses the index range query.
After disabling the subquery decorrelation rule, you can see `range: decided by [eq(test.t2.b, test.t1.b)]` in `operator info` of `IndexRangeScan_42(Build)`. It means that the decorrelation of correlated subquery is not performed and TiDB uses the index range query.
8 changes: 4 additions & 4 deletions explain-subqueries.md
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Expand Up @@ -67,11 +67,11 @@ EXPLAIN SELECT * FROM t1 WHERE id IN (SELECT t1_id FROM t2);
+--------------------------------+----------+-----------+------------------------------+---------------------------------------------------------------------------------------------------------------------------+
```

From the query results above, you can see that TiDB uses the index join operation `| IndexJoin_14` to join and transform the subquery. In the execution plan, the execution process is as follows:
From the query results above, you can see that TiDB uses the index join operation `IndexJoin_15` to join and transform the subquery. In the execution plan, the execution process is as follows:

1. The index scanning operator `└─IndexFullScan_31` at the TiKV side reads the values of the `t2.t1_id` column.
2. Some tasks of the `└─StreamAgg_39` operator deduplicate the values of `t1_id` in TiKV.
3. Some tasks of the `├─StreamAgg_49(Build)` operator deduplicate the values of `t1_id` in TiDB. The deduplication is performed by the aggregate function `firstrow(test.t2.t1_id)`.
1. The index scanning operator `└─IndexFullScan_26` at the TiKV side reads the values of the `t2.t1_id` column.
2. Some tasks of the `└─StreamAgg_34` operator deduplicate the values of `t1_id` in TiKV.
3. Some tasks of the `├─StreamAgg_44(Build)` operator deduplicate the values of `t1_id` in TiDB. The deduplication is performed by the aggregate function `firstrow(test.t2.t1_id)`.
4. The operation results are joined with the primary key of the `t1` table. The join condition is `eq(test.t1.id, test.t2.t1_id)`.

## Inner join (unique subquery)
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