Need help - SQL Server String Concatenation with Null

Question

Need help - SQL Server String Concatenation with Null

Qira

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Points: 1930
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August 21, 2014 at 8:46 am

#397235

I've table and data as following,
CREATE TABLE [dbo].[t_A1](
[idx] [int] NULL,
[batch_Id] [uniqueidentifier] NULL,
[JobNoticeID] [int] NULL,
[LevelID] [int] NULL,
[StudyFieldID] [int] NULL,
[min_CGPA] [int] NULL,
[max_CGPA] [int] NULL,
[Description] [nvarchar](10) NULL
) ON [PRIMARY]
GO
INSERT [dbo].[t_A1] ([idx], [batch_Id], [JobNoticeID], [LevelID], [StudyFieldID], [min_CGPA], [max_CGPA], [Description]) VALUES (-2147483635, N'df4771d6-84d3-4958-940d-aa54aa56cb0b', 76, 2, 36, 2, 4, N'OR')
INSERT [dbo].[t_A1] ([idx], [batch_Id], [JobNoticeID], [LevelID], [StudyFieldID], [min_CGPA], [max_CGPA], [Description]) VALUES (-2147483634, N'df4771d6-84d3-4958-940d-aa54aa56cb0b', 76, 1, 4, 2, 4, N'AND')
INSERT [dbo].[t_A1] ([idx], [batch_Id], [JobNoticeID], [LevelID], [StudyFieldID], [min_CGPA], [max_CGPA], [Description]) VALUES (-2147483591, N'df4771d6-84d3-4958-940d-aa54aa56cb0b', 76, 11, NULL, NULL, NULL, N'[END]')
My SQL as follow,
select idx,
'[LevelID]=' + Convert(varchar(20),LevelID) + ' AND [StudyField]='
+ Convert(varchar(20),StudyFieldID) + ' AND [CGPA] >='
+ Convert(varchar(20),min_CGPA) + ' AND [CGPA] <='
+ Convert(varchar(20),min_CGPA) + ' ' + Description as Expression
from t_A1
This is my result
idxExpression
-2147483635[LevelID]=2 AND [StudyField]=36 AND [CGPA] >=2 AND [CGPA] <=2 OR
-2147483634[LevelID]=1 AND [StudyField]=4 AND [CGPA] >=2 AND [CGPA] <=2 AND
-2147483591NULL
It's suppose to be,
idxExpression
-2147483635[LevelID]=2 AND [StudyField]=36 AND [CGPA] >=2 AND [CGPA] <=2 OR
-2147483634[LevelID]=1 AND [StudyField]=4 AND [CGPA] >=2 AND [CGPA] <=2 AND
-2147483591[LevelID]=11 AND [StudyField]=NULL AND [CGPA] >=NULL AND [CGPA] <=NULL [END]
How to fix my SQL? Please help

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Luis Cazares SSC Guru Points: 183698 More actions · Answer 1

If you concatenate anything to NULL, it will return NULL. The same way as if you try to do an arithmetic operation with NULL.

You can validate for nulls.

select idx,

'[LevelID]=' + ISNULL( Convert(varchar(20),LevelID), 'NULL') + ' AND [StudyField]'

+ ISNULL( Convert(varchar(20),StudyFieldID), 'NULL') + ' AND [CGPA] >='

+ ISNULL( Convert(varchar(20),min_CGPA), 'NULL') + ' AND [CGPA] <='

+ ISNULL( Convert(varchar(20),min_CGPA), 'NULL') + ' ' + Description as Expression

from t_A1

Remember that nothing is equal to NULL, so you can go a little further:

select idx,

'[LevelID]' + ISNULL( ' = ' + Convert(varchar(20),LevelID), ' IS NULL') + ' AND [StudyField]='

+ ISNULL( ' = ' + Convert(varchar(20),StudyFieldID), ' IS NULL') + ' AND [CGPA] '

+ ISNULL( ' >= ' + Convert(varchar(20),min_CGPA), ' IS NULL') + ' AND [CGPA] '

+ ISNULL( ' <= ' + Convert(varchar(20),min_CGPA), ' IS NULL') + ' ' + Description as Expression

from t_A1

Luis C.
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