# Operators In Execution Plan (Continue...)

+ Hash Aggregate Examples
  + `mysql> EXPLAIN SELECT /*+ HASH_AGG() */ count(*) FROM t;` 
```
+---------------------------+----------+-----------+---------------+---------------------------------+
| id                        | estRows  | task      | access object | operator info                   |
+---------------------------+----------+-----------+---------------+---------------------------------+
| HashAgg_9                 | 1.00     | root      |               | funcs:count(Column#4)->Column#3 |
| └─TableReader_10          | 1.00     | root      |               | data:HashAgg_5                  |
|   └─HashAgg_5             | 1.00     | cop[tikv] |               | funcs:count(1)->Column#4        |
|     └─TableFullScan_8     | 10055.00 | cop[tikv] | table:t       | keep order:false                |
+---------------------------+----------+-----------+---------------+---------------------------------+
4 rows in set (0.01 sec)
```
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Hash Aggregate Examples
Hash Aggregate operator
The Hash Aggregation operator is optimized for multi-threaded concurrency and performs quickly, but consumes a lot of memory. With the HASH_AGG hint, we can force the execution plan to go through the hash aggregate operator.
```
mysql> EXPLAIN SELECT /*+ HASH_AGG() */ count(*) FROM t;
+---------------------------+----------+-----------+---------------+---------------------------------+
| id                        | estRows  | task      | access object | operator info                   |
+---------------------------+----------+-----------+---------------+---------------------------------+
| HashAgg_9                 | 1.00     | root      |               | funcs:count(Column#4)->Column#3 |
| └─TableReader_10          | 1.00     | root      |               | data:HashAgg_5                  |
|   └─HashAgg_5             | 1.00     | cop[tikv] |               | funcs:count(1)->Column#4        |
|     └─TableFullScan_8     | 10055.00 | cop[tikv] | table:t       | keep order:false                |
+---------------------------+----------+-----------+---------------+---------------------------------+
4 rows in set (0.01 sec)
```