# Data Scaner Operators (Continue...)

+ `Hash Join` example
  + `EXPLAIN SELECT /*+ HASH_JOIN(t1, t2) */ * FROM t1, t2 WHERE t1.id = t2.id;` 
```
+-----------------------------+-----------+-----------+---------------+------------------------------------------------+
| id                          | estRows   | task      | access object | operator info                                  |
+-----------------------------+-----------+-----------+---------------+------------------------------------------------+
| HashJoin_27                 | 142020.00 | root      |               | inner join, equal:[eq(test.t1.id, test.t2.id)] |
| ├─TableReader_29(Build)     | 142020.00 | root      |               | data:TableFullScan_28                          |
| │ └─TableFullScan_28        | 142020.00 | cop[tikv] | table:t1      | keep order:false                               |
| └─TableReader_31(Probe)     | 180000.00 | root      |               | data:TableFullScan_30                          |
|   └─TableFullScan_30        | 180000.00 | cop[tikv] | table:t2      | keep order:false                               |
+-----------------------------+-----------+-----------+---------------+------------------------------------------------+
5 rows in set (0.00 sec)
```

------------------------------------------------------------
Hash join example
```
EXPLAIN SELECT /*+ HASH_JOIN(t1, t2) */ * FROM t1, t2 WHERE t1.id = t2.id;

 
+-----------------------------+-----------+-----------+---------------+------------------------------------------------+
| id                          | estRows   | task      | access object | operator info                                  |
+-----------------------------+-----------+-----------+---------------+------------------------------------------------+
| HashJoin_27                 | 142020.00 | root      |               | inner join, equal:[eq(test.t1.id, test.t2.id)] |
| ├─TableReader_29(Build)     | 142020.00 | root      |               | data:TableFullScan_28                          |
| │ └─TableFullScan_28        | 142020.00 | cop[tikv] | table:t1      | keep order:false                               |
| └─TableReader_31(Probe)     | 180000.00 | root      |               | data:TableFullScan_30                          |
|   └─TableFullScan_30        | 180000.00 | cop[tikv] | table:t2      | keep order:false                               |
+-----------------------------+-----------+-----------+---------------+------------------------------------------------+
5 rows in set (0.00 sec)
```
Hash join operator
The Hash Join operator is optimized for multiple threads and performs faster, but consumes more memory. In Hash Join China, the data of the build segment is cached in memory, and a hash table is constructed based on the data. The data of the probe segment is then read, and the data of the probe segment is used to probe the hash table constructed by the build segment. As with other database products, since the data is hashed, a hash join can only exist in an equivalent query.