Embarassing Question : checking for NULL

[datadriven]

There a table column I need to math results when NULL exists:

SELECT *
FROM Mem LEFT JOIN Run on Run.fk_MID=Mem.MID
WHERE Run.PAID='NULL'

But how does this really go? And yes, this is embarassing to ask.
Records having NULL for this column will not appear, for example, when they exist and when checking on

Run.PAID<> 2
Run.PAID!=2

As another example:

SELECT *
FROM Mem, Run
WHERE fk_MID=MID AND PAID=2 AND MID!=366

Does return to right results, whereas this does not (returns no results):

SELECT *
FROM Mem, Run
WHERE fk_MID =MID AND PAID!=2 AND MID!=366

What could be happening?

[Imminent]

You're using some operators incorrectly.

When checking for null values you need to use the 'IS' operator. E.g:

WHERE SomeField IS NULL
WHERE SomeField IS NOT NULL

The not equals operator is actually <>. E.g.

WHERE SomeField <> SomeOtherField

Your queries should be:

SELECT
	*
FROM
	Mem
LEFT JOIN
	Run ON Run.fk_MID = Mem.MID
WHERE
	Run.PAID IS NULL

SELECT
	*
FROM
	Mem
LEFT JOIN
	Run ON Run.fk_MID = Mem.MID
WHERE
	Run.PAID <> 2 AND Mem.MID <> 366

[r937]

imminent, nice reply, absolutely correct about the NULLs

just one minor detail about your sample queries -- in a LEFT OUTER JOIN, if you have a WHERE condition on a column of the right table, this effectively changes the LEFT OUTER JOIN into an INNER join because it can no longer return unmatched rows from the left table

your last example should say:

select *
  from Mem
left outer
  join Run 
    on Run.fk_MID = Mem.MID
   and Run.PAID <> 2 
 where Mem.MID <> 366

[datadriven]

Thank You Imminent, Rudy,

Works Great.

Rudy- Then, that Left Outer Join I see too could be a way of verifying that values are being correctly inserted into both desired tables (visual check)

Only other comment I have is that operator != seems to work as <>does for values other than NULL. (But my oberservation sounds inherently risky for some reason)

[Imminent]

imminent, nice reply, absolutely correct about the NULLs

just one minor detail about your sample queries

Ah yes, good point. Probably should've spent a bit more time trying to understand the intention of the query