Turning an N:N join into several 1:N?

Question

I have one table/folder containing the following items:
activity_id, industry_id, and product_id.
I have another table containing the values (e.g. description of the activity, description of the industry and description of the product) of the id's. The columns in this table are pid, id, and description. In other words: the description of activity, industry and product is kept in the same column. The pid tells whether the column reflects activity, industry or product. So by example I have the following rows:
pid, id, description
2, 3, Business Work
2, 4, Leave
3, 5, Software Industry
3, 7, Manufacturing
4, 9, Large Shoes
4, 10, Small Shoes
So rows 1-2 is about activities, rows 3-4 is about industry, and rows 5-6 is about products.
I want the joins to look up the description, but how do I establish the join?
The activity_id should join with the rows that contain
2,3, Business Work
2,4, Leave
and the industry_id should join with the rows that contain
3, 5, Software Industry
3, 7, Manufacturing
and the product_id should join with the rows that contain
4,9, Large Shoes
4,10 Small Shoes
Thanks

Answer 1

You could try to type this:
select pid,id,description from table1 left join table2 on (table1.activity_id=table2.activity_id) and (table1.industry_id=table2.industry_id)
and (table1.product_id=table2.product_id);
Table1 is the table where activity_id,industry_id and product_id is saved. This table must be the master.The second table is where the values are saved and must be the detail table.
Hope this helps.