Question

I was wondering when having a parent table and a child table with foreign key like:

users
id | username | password |

users_blog
id | id_user | blog_title

is it ok to use id as auto increment also on join table (users_blog) or will i have problems of query speed?

also i would like to know which fields to add as PRIMARY and which as INDEX in users_blog table?

hope question is clear, sorry for my bad english 😛

Answer 1

I don’t think you actually need the id column in the users_blog table. I would make the id_user the primary index on that table unless you have another reason for doing so (perhaps the users_blog table actually has more columns and you are just not showing it to us?).

As far as performance, having the id column in the users_blog table shouldn’t affect performance by itself but your queries will never use this index since it’s very unlikely that you’ll ever select data based on that column. Having the id_user column as the primary index will actually be of benefit for you and will speed up your joins and selects.