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Setting a NULL value to an empty string in SQL

Heyas,

I have the following query:

SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd));

If this SET statement returns a NULL value is their way to change  'f3.DBWCode' field to an empty string ''.

Any assistance is always appreciated.

Thank you.
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Zack
Asked:
Zack
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2 Solutions
 
KarenAnalyst programmerCommented:
COALESCE(f3.DBWCode, '')
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Pawan KumarDatabase ExpertCommented:
You can use below..

ISNULL(f3.DBWCode, '')
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ZackGeneral IT Goto GuyAuthor Commented:
Heyas,

Can you be a bit more descriptive as to how I would use these?

Thank you.
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Pawan KumarDatabase ExpertCommented:
Hi,

Please find the usage below.

ISNULL

SELECT Col1, ISNULL(Col2,0) Col2
FROM TableName

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SELECT Col1, ISNULL(Col2,'') Col2
FROM TableName

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COALESCE

SELECT Col1 , COALESCE(Col2,0) Col2
FROM TableName

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SELECT Col1 , COALESCE(Col2,'') Col2
FROM TableName

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Definition -

ISNULL - Replaces NULL with the specified replacement value.

ISNULL ( check_expression , replacement_value )  

From MSDN - The value of check_expression is returned if it is not NULL; otherwise, replacement_value is returned after it is implicitly converted to the type of check_expression, if the types are different. replacement_value can be truncated if replacement_value is longer than check_expression.

COALESCE - Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.

COALESCE ( expression [ ,...n ] )  

FROM MSDN -

The COALESCE expression is a syntactic shortcut for the CASE expression. That is, the code COALESCE(expression1,...n) is rewritten by the query optimizer as the following CASE expression:
CASE
WHEN (expression1 IS NOT NULL) THEN expression1
WHEN (expression2 IS NOT NULL) THEN expression2
...
ELSE expressionN
END

REF [ https://msdn.microsoft.com/en-in/library/ms190349.aspx ]
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KarenAnalyst programmerCommented:
hmm... hang on, do you mean
If this SET statement returns a NULL value
or
If this SELECT statement returns a NULL value
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ZackGeneral IT Goto GuyAuthor Commented:
Hi Snowberry,

Clarification: If this SET statement returns a NULL value.

Thank you.
0
 
Pawan KumarDatabase ExpertCommented:
May be..this

SET Environment.Variables.flag3 = ISNULL (SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 
									WHERE f3.ItemName='presendonadmit' 
									AND f3.DBWCode=InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd) , '' )

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Pawan KumarDatabase ExpertCommented:
Or you can check like below..after SET,...

ISNULL ( Environment.Variables.flag3 , '' )
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KarenAnalyst programmerCommented:
ok, in that case your "subject" confused me

IF Environment.Variables.flag3 IS NULL THEN
    UPDATE Database.WMB_DBW_SAP_CODE as f3 SET f3.DBWCode = '' WHERE f3.ItemName='presendonadmit' 

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ZackGeneral IT Goto GuyAuthor Commented:
Hi Pawan,

Thank for the input but I what I need is just the ISNULL to filter just on the f3.DBWCode field see below for a pseudocode example.

SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=ISNULL(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd),'');

Thank you.
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ZackGeneral IT Goto GuyAuthor Commented:
Hi Snowberry,

My apologies to you I just re-read my question I didn't make it 100% clear what I require is something like this:

SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=ISNULL(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd),'');

How I filter just on the f3.DBWcode field for ISNULL?

Thank you.
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Pawan KumarDatabase ExpertCommented:
So do you need records where f3.DBWcode IS NULL ?
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Pawan KumarDatabase ExpertCommented:
may be..

SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=ISNULL(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd),'');

AND f3.DBWCode IS NULL
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KarenAnalyst programmerCommented:
Do you want to do the following, but in only one statement?

SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd));
IF Environment.Variables.flag3 IS NULL THEN
    SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=''));

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Pawan KumarDatabase ExpertCommented:
Or may be...this

SET Environment.Variables.flag3 = 

CASE WHEN (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd)) IS NULL
THEN 
	(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=''));
END

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ZackGeneral IT Goto GuyAuthor Commented:
Hi Pawan,

Yes, I need the SET statement to flag when  f3.DBWCode ISNULL and change it to ''.

Thank you.
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KarenAnalyst programmerCommented:
Do you want to know when  f3.DBWCode is NULL, or when Environment.Variables.flag3 is NULL ??????
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Pawan KumarDatabase ExpertCommented:
Didnt get can you explain via Pesudo code?
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ZackGeneral IT Goto GuyAuthor Commented:
Hi Snowberry,

When f3.DBWCode  ISNULL in the SET Statement: SET Environment.Variables.flag3 =(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd));

My apologies for the lack of clarification initially.

Thank you.
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Pawan KumarDatabase ExpertCommented:
May be this

SET Environment.Variables.flag3 = 
    	
	(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND ISNULL(f3.DBWCode , 
	
	(THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=''))

	=InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd))

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Pawan KumarDatabase ExpertCommented:
SET Environment.Variables.flag3 =
          
      (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND ISNULL(f3.DBWCode ,
      
      (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode=''))

      =InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd))


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KarenAnalyst programmerCommented:
it is really unclear what you want

lets try an example

if there is a record in f3 table

InvCode = 123
ItemName = 'presendonadmit'
DBWCode = 456

then your query will return 123 if InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd = 456

So what problem are you trying to cope with ?
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ZackGeneral IT Goto GuyAuthor Commented:
Hi Snowflake,

The best way I can clarify is if 'InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd' ISNULL change to ''.

Thank you.
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Pawan KumarDatabase ExpertCommented:
Ok try this then


SET Environment.Variables.flag3 =

 (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND f3.DBWCode= ISNULL(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd,'')))
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Pawan KumarDatabase ExpertCommented:
or you need like below

SET Environment.Variables.flag3 =

 (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND ISNULL(f3.DBWCode,'')= ISNULL(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd,'')))
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KarenAnalyst programmerCommented:
so

if there is a record in f3 table

InvCode = 123
ItemName = 'presendonadmit'
DBWCode = 456

then you want your query to return 123 if InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd IS NULL


OR


if there is a record in f3 table

InvCode = 123
ItemName = 'presendonadmit'
DBWCode = ''

then you want your query to return 123 if InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd IS NULL
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ZackGeneral IT Goto GuyAuthor Commented:
Hi Snowflake

Correction:

so

if DBWCode equals NULL

InvCode = 123
ItemName = 'presendonadmit'
DBWCode = NULL

Then I want DBWCode to be:

InvCode = 123
ItemName = 'presendonadmit'
DBWCode = ''

I think SET Environment.Variables.flag3 =

 (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND ISNULL(f3.DBWCode,'')= ISNULL(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd,'')))

Posted by Pawan will work I will try in the next hr.

Thanks.
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KarenAnalyst programmerCommented:
are you saying you want to update the database????
your last comment does not make any sense
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Pawan KumarDatabase ExpertCommented:
I think he wanted to compare these fields and WHEN both are NULL then the comparison was failing.

Now when we are replacing NULLs with '' the comparison will happen.

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KarenAnalyst programmerCommented:
Hopefully you are right Pawan!

By the way, since he is using ESQL I do not think ISNULL will work. But COALESCE should.
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Pawan KumarDatabase ExpertCommented:
Ohhh yes thanks , great sir... Let me rewrite the query for him.

SET Environment.Variables.flag3 =

 (THE(SELECT ITEM f3.InvCode FROM Database.WMB_DBW_SAP_CODE as f3 WHERE f3.ItemName='presendonadmit' AND COALESCE(f3.DBWCode,'')= COALESCE(InputRoot.MRM.ns:DG1[3].ns:DG26PresentOnAdmissionInd,'')))
1
 
ZackGeneral IT Goto GuyAuthor Commented:
Thank you very much for the help guys.
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