MySQL 8.0.18 Hash Join does not support left/right join left and right join issues

In MySQL 8.0.18, a new Hash Join function was added, which is applicable to fields that are not indexed and can perform equal-value association queries. In previous versions, if the connected fields were not indexed, the query speed would be very slow and the optimizer would use the BNL (block nested) algorithm.

The Hash Join algorithm stores the data of a small table in a hash table in memory, matches the data in the large table row by row, calculates the hash value, and returns the qualified data from the memory to the client.

Use sysbench to generate four tables and delete the default k-field index.

We can use explain format=tree command to see that the hash join algorithm has been used.

However, the current version 8.0.18 only supports join. Left join and right join are invalid, please note this.

Summarize

The above is what I introduced to you about the MySQL 8.0.18 Hash Join not supporting left/right join. I hope it will be helpful to you. If you have any questions, please leave me a message and I will reply to you in time. I would also like to thank everyone for their support of the 123WORDPRESS.COM website!
If you find this article helpful, please feel free to reprint it and please indicate the source. Thank you!