How can I compare 2 columns in 2 tables to check for UNEQUAL values

Question

I have a table say Table 1 with column A with values {22,18,17} and another table Table 2 with column B with values {18,22} when I do a query like

select * from Table 1 where column A not in (select column B in Table 2).

This gives me 3 rows {22,18,17}

I want only 17 as output.

I am newbie to SQL can anyone help me

Thanks - and **please** for future questions: **always** provide those crucial bits of information right away, when you post the qusetion! — marc_s, Aug 12 '11 at 18:57

TrevDev · Accepted Answer · 2011-08-16T06:17:12.983

2

SELECT * FROM Table1 as T1
LEFT JOIN Table2 as T2 on T1.ColumnA = T2.ColumnB
WHERE T2.T2ID IS NULL

edited Aug 16 '11 at 06:17

answered Aug 12 '11 at 18:50

TrevDev

This is not more efficient than `NOT IN` / `NOT EXISTS`. See http://sqlinthewild.co.za/index.php/2010/03/23/left-outer-join-vs-not-exists/ – Martin Smith Aug 12 '11 at 23:02

1 Answers1