Question

Let’s say I have two identical tables, A and B, with the row “x”.

I want to select all elements in A, where the value of x in A is not in any value of x of B.

How do I do that?

Answer 1

You could also do something like this:

SELECT * FROM TableA
LEFT JOIN TableB on TableA.X = TableB.X
WHERE TableB.X IS NULL

_{(For the very straightforward example in your question, a NOT EXISTS / NOT IN approach is probably preferable, but is your real query is more complex, this is an option you might want to consider; if, for instace, you want som information from TableB where there is a match, but also want to know where there isn’t one)}