How can I join two tables with different number of rows in MySQL?

Question

I have two tables which I want to connect.

TABLE_A:

+-----------+-----------+---------+
| row_id    | category  | val_1   |
+-----------+----------         


        

Answer 1

If you want all the results, you need an outer join, not an inner one. (Inner only returns the rows where there is a match; outer returns all rows, with the matching rows "stitched together")