MySQL Hash index

When the big data Volume MyISAM engine table joins, MySQL only nest Loop way to operate, the efficiency is very low.

Therefore, the hash index should be used at this time.

Since only the memory and NDB engines support hash indexes, they should be used as cache tables.

For example:

CREATE temporary TABLE T1 engine=memory as SELECT * from TABLEA;

ALTER TABLE T1 ADD INDEX T1 (ID) USING HASH;

CREATE temporary TABLE T2 engine=memory as SELECT * from TABLEB;

ALTER TABLE T2 ADD INDEX T1 (ID) USING HASH;

select* from T1 INNER joins T2 on T1.id=t2.id.

DROP TABLE T1;

DROP TABLE T2;

The greater the amount of data, the more efficient the increase is.

MySQL Hash index