why do these queries produce different results?

Question

I have run these two queries that look like they do the same thing, but give different results:

SELECT COUNT(stage1) AS total 
FROM progress_status 
WHERE stage1 = 3 
AND stage2 != 3 AND stage3 !=3 AND stage4 !=3 AND stage5 !=3;

# total = 90

SELECT COUNT(stage1) AS total 
FROM progress_status 
WHERE stage1 = 3 
AND (stage2,stage3,stage4,stage5) != (3,3,3,3)

# total = 314

Answer 1

The second one is doing:

AND (stage2 != 3 OR stage3 !=3 OR stage4 !=3 OR stage5 !=3);

Answer 2

It's normal:

• Your first query asks all stage columns to be different from 3
• Your second query asks those columns not beeing equal to 3 at the same time, so if one is different from 3 record is taken! This query is like you're using OR in your WHERE clause.