# SQL 语句执行计划不准 - 执行计划

+ 在 TiKV 端分别对表 a 和 b 的数据进行扫描，其中 `TableScan_16` 扫描了 1.46 亿的行数

```
+----------------------------+--------------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id                         | count        | task | operator info                                                                                                                                                     |
+----------------------------+--------------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| StreamAgg_13               | 1.00         | root | funcs:count(1)                                                                                                                                                    |
| └─HashRightJoin_27         | 421.12       | root | inner join, inner:TableReader_18, equal:[eq(a.fund_code, b.fund_code)]                                                                                            |
|   ├─TableReader_18         | 421.12       | root | data:Selection_17                                                                                                                                                 |
|   │ └─Selection_17         | 421.12       | cop  | eq(a.pay_confirm_status, 1), eq(a.status, "CANCEL_SUCCESS"), gt(a.updated_at, 2020-03-03 22:31:08), in(a.type, "PURCHASE", "APPLY"), not(isnull(a.cancel_app_no)) |
|   │   └─TableScan_16       | 145920790.55 | cop  | table:a, range:[177045000,+inf], keep order:false                                                                                                                 |
|   └─TableReader_37         | 6442.00      | root | data:TableScan_36                                                                                                                                                 |
|     └─TableScan_36         | 6442.00      | cop  | table:b, range:[-inf,+inf], keep order:false                                                                                                                      |
+----------------------------+--------------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
```

-------------------------------------------------------------
```
mysql> explain 
    -> select count(*)
    -> from tods.bus_jijin_trade_record a,   tods.bus_jijin_info b 
    -> where a.fund_code=b.fund_code  and a.type in ('PURCHASE','APPLY')  
    -> and a.status='CANCEL_SUCCESS' and   a.pay_confirm_status = 1 
    -> and a.cancel_app_no is not null and   a.id >=  177045000  
    -> and a.updated_at >   date_sub(now(), interval 48 hour) ;
+----------------------------+--------------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id                         | count        | task | operator info                                                                                                                                                     |
+----------------------------+--------------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| StreamAgg_13               | 1.00         | root | funcs:count(1)                                                                                                                                                    |
| └─HashRightJoin_27         | 421.12       | root | inner join, inner:TableReader_18, equal:[eq(a.fund_code, b.fund_code)]                                                                                            |
|   ├─TableReader_18         | 421.12       | root | data:Selection_17                                                                                                                                                 |
|   │ └─Selection_17         | 421.12       | cop  | eq(a.pay_confirm_status, 1), eq(a.status, "CANCEL_SUCCESS"), gt(a.updated_at, 2020-03-03 22:31:08), in(a.type, "PURCHASE", "APPLY"), not(isnull(a.cancel_app_no)) |
|   │   └─TableScan_16       | 145920790.55 | cop  | table:a, range:[177045000,+inf], keep order:false                                                                                                                 |
|   └─TableReader_37         | 6442.00      | root | data:TableScan_36                                                                                                                                                 |
|     └─TableScan_36         | 6442.00      | cop  | table:b, range:[-inf,+inf], keep order:false                                                                                                                      |
+----------------------------+--------------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
```

在类似这样的查询中，可能会出现执行计划不准的情况，比如这个查询的执行计划。
TableScan_16，TableScan_36：表示在 TiKV 端分别对表 a 和 b 的数据进行扫描，其中 TableScan_16 扫描了 1.46 亿的行数；
Selection_17：表示满足表 a 后面 where 条件的数据；
TableReader_37： 由于表 b 没有独立的附加条件，所以直接将这部分数据返回给 TiDB；
TableReader_18：将各个 coprocessor 满足 a 表条件的结果返回给 TiDB；
HashRightJoin_27：将 TableReader_37 和 TableReader_18 上的结果进行 hash join；
StreamAgg_13：进一步统计所有行数，将数据返回给客户端；