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Databases

Eylon Cohen
Eylon Cohen
4,779 Points
Posted by Eylon Cohen
Eylon Cohen
4,779 Points

Joining the same table (on different column) in order to screen out more resoluts ?

Hello, I will explain my question with a basic example:

I have table 1 with the colums ID, A and B (all int). I have table 2 with the column ID (int of course). I would like to produce a table (using SELECT) showing the IDs of the lines from table 1 that the values in both their column A and B cells are IDs from table 2 (value in A can be different than value in B, but both are from table 2).

If it was only one column I would of course use a simple Join. but with 2 columns I'm not sure what to do. I know I can use a subquery, but I was wondering if there is a simple way to do that, without a subquery.

Thank you!

1 Answer

Steven Parker
Steven Parker
231,128 Points
Steven Parker
Steven Parker
231,128 Points

You can have two JOINs of the same tables with different criteria:

SELECT t.* FROM table1 t
JOIN table2 x ON t.A = x.ID
JOIN table2 y ON t.B = y.ID

Now please tell me I did not just do your homework. :open_mouth: