In MySQL 8.0.18, an increase of Hash Join new features, it is suitable for field index is not created, do the equivalent relational query. In previous versions, if the field is not connected to create the index, query speed will be very slow, the optimizer will use BNL (nesting block) algorithm.
Hash Join algorithm to the data table stored in a small memory hash table, and the data line by line to match the large table, the hash value is calculated and the qualified data, returned from the client memory.
Generates four tables with sysbench, and delete the default field index k.
We explain format = tree command to view has been used to hash join algorithm.
But the current 8.0.18 version only supports join. left join and right join failure, please pay attention here.
