Does NULL <> 'string'?

Jeremy Falcon

Some are... so I'm told. :rolleyes:

Jeremy Falcon

TheGreatAndPowerfulOz

They don't all "enjoy" it. It's a job. Indeed, prostitutes go same-sex for their personal one-on-ones because opposite-sex has lost all appeal due to the "job".

#SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

Jagger B

Sorry, You failed the interview. He'll call you next time. :|

Jeremy Falcon

So wait, you're saying I can't be a prostitute? Why? Because I'm a guy? That's discrimination.

Jeremy Falcon

Jagger B

Are you saying, Sql Dev's = prostitute?

Jeremy Falcon

Yes. Everyone knows you have go through prostitute training to get certified. You just finding this out? You may wanna talk to your MS rep.

Jeremy Falcon

Nelek

OriginalGriff wrote:

Dali-esque

Surrealistic? or womenizer? :laugh: :laugh: :laugh: :laugh:

M.D.V. ;) If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about? Help me to understand what I'm saying, and I'll explain it better to you Rating helpful answers is nice, but saying thanks can be even nicer.

Nelek

Guys... this is not the soapbox

M.D.V. ;) If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about? Help me to understand what I'm saying, and I'll explain it better to you Rating helpful answers is nice, but saying thanks can be even nicer.

txmrm

Like everything else in programming, it depends. In this case it depends on the SQL ansi_nulls setting. If this is a statement inside a SQL stored procedure, view, etc the ansi_nulls setting is burned into the object when it is created. If this is an ad-hoc statement then the ansi_nulls setting in effect for the SQL connection the statement is executed against is used. If you want null <> 'value' to return true, you could just set ansi_nulls off. Not that I would recommend doing that...

Richard Deeming

txmrm wrote:

Not that I would recommend doing that...

Especially as it's deprecated, and likely to be removed:

SET ANSI_NULLS (Transact-SQL) | Microsoft Docs[^]:

In a future version of SQL Server, ANSI_NULLS will always be ON and any applications that explicitly set the option to OFF will generate an error. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Kornfeld Eliyahu Peter

It may be weird, but it's nothing new... I learned SQL on mainframe, and the first thing we had to memorize about NULL is that it can not stand of either side of any of the comparison operators (=, <, >, <>)...

Skipper: We'll fix it. Alex: Fix it? How you gonna fix this? Skipper: Grit, spit and a whole lotta duct tape.

obermd

The SQL standards don't define how NULL should behave. What you found is accurate for one SQL dialect but may not be accurate for another. This is actually one of the biggest challenges when changing RDBMS vendors.

agolddog

Total guess here, but I wonder if the SQL engine errors on the side of caution. Something like: "I don't have a string to compare to. Thus, I can't say with certainty it is or is not 'value', so I'll return false." But yeah, I think that has gotten us all at one time or another when doing inequality in a query. I also wonder if it varies with different implementations of SQL. But not enough to, you know, test it or anything.

Member_5893260

...except there's an "or" in there: logically, it shouldn't matter: if it's null, at least one of the conditions is true. I have a feeling that "null=string" evaluates to null, and then "field is null" evaluates to Boolean, then "boolean or null" evaluates to null, which is why it doesn't work. But that's somewhat abstruse. Which server is this: is it SQL Server or MySQL... or perhaps something else?

Lost User

But the IS NULL check is made on TableTwo.TableTwoID While string compare is made with TableTwo.StringColumn So I see no incorrect handling, but of course it is not very intuitiv.

Kirk 10389821

You stumbled on the NULL value special case. NOTHING can be compared to NULL. In fact NULL <> NULL... ISNULL() is the correct way, or (X IS NULL) It makes for difficult code to write with dynamic where clauses on nullable fields. I have seen SOME DBs that they treat '' as NULL and it is worse with a varchar field that trims trailing spaces, and someone stores a space. This is BY DESIGN as explained, and part of the "CALCULUS" of the system. ALSO (1 = NULL) is NOT false... It is NULL That prevents inverting the logic to "NOT (1 = NULL)" Learn that ONCE, learn it well, and life becomes easier.

Chris Maunder

I've learned it many time. My brain, however, refuses to store it in long term memory.

cheers Chris Maunder

Gary Wheeler

Nelek wrote:

womenizer?

My experience is that SQL lacks, er, discrimination in who it molests.

Software Zen: delete this;

Richard Deeming

Dan Sutton wrote:

I have a feeling that "null=string" evaluates to null, and then "field is null" evaluates to Boolean, then "boolean or null" evaluates to null, which is why it doesn't work.

Pretty much, but it depends on the operator and the boolean value. If it's possible to short-circuit the operator, it doesn't matter if one condition is Null.

AND | True | False | Null

OR | True | False | Null

It's sometimes easier to think of Null as "unknown". :)

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Member_5893260

Yeah - you're right. Hadn't had coffee yet. LOL!