# `HashJoin` Operator

__*Echo Build Side, Probe Side to execution plan part*__

+ Build a hash table in memory on the `build side`
+ Read the data to probe the hash table on the `probe side`

![`smart`](HashJoin01_aa_002_20230912.png)

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The `HashJoin` operation starts by selecting the table with the fewer rows as the driving table based on statistics. In the slide, the `employees` table, having fewer rows, is chosen as the driving table. This table is then loaded into the cache of the TiDB Server.