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''=0 ?!?!


''=0 ?!?!

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Alan Burstein
Alan Burstein
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This is something I ran into today and am curious if anyone knows anything about this....

I was working on something earlier and executed T-SQL command. I noticed a typo in my code after the query had executed successfully. The offending code looked something like this...

IF CHARINDEX('xxx','yy')=''
PRINT 'xxx'



Though logic would dictate otherwise, the above query runs successfully on 2008 & 2012. It appears that SQL Server treats double single quotes as a zero (0). I was curious so I ran these:


SELECT ISNUMERIC(5);
SELECT ISNUMERIC('');



The first statement returned a 1, the second returned a 0. This is what I expected: 5 is numeric, '' is not. Satisfied.

Then I ran the following and it appears that ''=0...

SELECT 7*''
SELECT CAST('' AS int)
SELECT REPLICATE(CAST('' AS int),5)



After a bunch of Google searching I was not able to find anything about this... Blink

Is this a bug, is my server haunted? Anyone know anything about this?

-- Alan Burstein


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GilaMonster
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SQL cannot compare two different data types, nor can it multiply by a string. Hence, any time you ask it to do that, it will do an implicit conversion. As you saw, casting '' to int results in 0 (it can't logically be anything else), so all you're seeing here is the implicit conversion of a string to an integer.

Gail Shaw
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SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Alan Burstein
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Thanks Gail.

-- Alan Burstein


Helpful links:

Best practices for getting help on SQLServerCentral -- Jeff Moden
How to Post Performance Problems -- Gail Shaw

Nasty fast set-based string manipulation functions:
For splitting strings try DelimitedSplit8K or DelimitedSplit8K_LEAD (SQL Server 2012+)
To split strings based on patterns try PatternSplitCM
Need to clean or transform a string? try NGrams, PatExclude8K, PatReplace8K, DigitsOnlyEE, or Translate8K

I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code. -- Itzik Ben-Gan 2001

dwain.c
dwain.c
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If you think those "typos" that pass SQL Server's parser seem weird, try this one:


SELECT 7+$





My mantra: No loops! No CURSORs! No RBAR! Hoo-uh!

My thought question: Have you ever been told that your query runs too fast?

My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.


Need to UNPIVOT? Why not CROSS APPLY VALUES instead?
Since random numbers are too important to be left to chance, let's generate some!
Learn to understand recursive CTEs by example.
Splitting strings based on patterns can be fast!
My temporal SQL musings: Calendar Tables, an Easter SQL, Time Slots and Self-maintaining, Contiguous Effective Dates in Temporal Tables
Alan Burstein
Alan Burstein
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dwain.c (12/17/2012)
If you think those "typos" that pass SQL Server's parser seem weird, try this one:


SELECT 7+$




Thanks for the post dwain. That's really odd too; I would never think to try that if not for this forum.. This was actually the first time I ever posted a question on any forumn - I decided to do so after you suggested it in a different thread recently (I wish I had a more interesting question to post).

I assumed that statement was casting 7 as money... I wanted to see for sure but couldn't think a way to do something like this:
SELECT GetTheDatatypeOf(7+$) Unsure

Then I came up with:

select 7+$ AS dt
into tmp;

SELECT DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME='tmp' AND COLUMN_NAME='dt';

DROP TABLE tmp;



Edit: Typo

-- Alan Burstein


Helpful links:

Best practices for getting help on SQLServerCentral -- Jeff Moden
How to Post Performance Problems -- Gail Shaw

Nasty fast set-based string manipulation functions:
For splitting strings try DelimitedSplit8K or DelimitedSplit8K_LEAD (SQL Server 2012+)
To split strings based on patterns try PatternSplitCM
Need to clean or transform a string? try NGrams, PatExclude8K, PatReplace8K, DigitsOnlyEE, or Translate8K

I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code. -- Itzik Ben-Gan 2001

ScottPletcher
ScottPletcher
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Interesting too is that an empty string does not work for decimal values:

SELECT 1.1+''

But it again does work for dates:

SELECT CAST('' as datetime)

Ah the wonders of SQL -- "wonder why it does that?!"

SQL DBA,SQL Server MVP(07, 08, 09) Prosecutor James Blackburn, in closing argument in the Fatal Vision murders trial:
If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them.
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