mysql update too slow when joining multiple tables
- by user293487
Hi,
I have two tables. they looks like as follows:
Id (int) Tags char(128).
the column Tags in table A does not have value. It is empty.
The column Tags in table B has value.
What I want to copy the Tags in table B to corresponding place of table A. the mapping is based on Id.
My sql query is:
update A
INNER JOIN B
set A.Tags = B.Tags
where A.Id = B.Id
There are about 2,000,000 rows in table A, and 50,000 rows in table B.
The update seems very slow.... Could anyone tell me how to make it run faster?
