Shulou(Shulou.com)06/01 Report--

In MySQL 8.0.18, a new function of Hash Join has been added, which is suitable for fields that have not been indexed and do equivalent association queries. In previous versions, if the joined fields were not indexed, the query speed would be very slow, and the optimizer would use the BNL (block nesting) algorithm.

The Hash Join algorithm stores a small table data 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 to the client from memory.

Generate 4 tables with sysbench and delete the default k-field index.

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

However, at present, version 8.0.18 only supports join. Left join and right join fail, please note here.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.