SQL Join Command Resulting in Duplicate Rows

If you find your JOIN command returning duplicate values and you’ve eliminated the usual suspects, check to see if the table being joined has a primary key. I had a 4 table JOIN statement where everything was fine when I did the first 3 JOINs, but once I added the 4th table, the results started returning multiple duplicate values. It turned out that table was missing a primary key.

After adding a primary key to the table, the query began functioning as expected.

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