Checking whether conditions are met by all rows with dynamic SQL - sql

Question

I have a table in SQL Server 2008 which contains custom validation criteria in the form of expressions stored as text, e.g.
StagingTableID CustomValidation
----------------------------------
1 LEN([mobile])<=30
3 [Internal/External] IN ('Internal','External')
3 ([Internal/External] <> 'Internal') OR (LEN([Contact Name])<=100)
...
I am interested in determining whether all rows in a table pass the conditional statement. For this purpose I am writing a validation stored procedure which checks whether all values in a given field in a given table meet the given condition(s). SQL is not my forte, so after reading this questions this is my first stab at the problem:
EXEC sp_executesql N'SELECT #passed = 0 WHERE EXISTS (' +
N'SELECT * FROM (' +
N'SELECT CASE WHEN ' + #CustomValidationExpr + N' THEN 1 ' +
N'ELSE 0 END AS ConditionalTest ' +
N'FROM ' + #StagingTableName +
N')t ' +
N'WHERE t.ConditionalTest = 0)'
,N'#passed BIT OUTPUT'
,#passed = #PassedCustomValidation OUTPUT
However, I'm not sure if the nested queries can be re-written as one, or if there is an entirely better way for testing for validity of all rows in this scenario?
Thanks in advance!

Answer 1

You should be able to reduce by at least one subquery like this:
EXEC sp_executesql N'SELECT #passed = 0 WHERE EXISTS (' +
N'SELECT 1 FROM ' + #StagingTableName +
N'WHERE NOT(' + #CustomValidationExpr + N')) ' +
,N'#passed BIT OUTPUT'
,#passed = #PassedcustomValidation OUTPUT

Answer 2

Before we answer the original question, have you looked into implementing constraints? This will prevent bad data from entering your database in the first place. Or is the point that these must be dynamically set in the application?
ALTER TABLE StagingTable
WITH CHECK ADD CONSTRAINT [StagingTable$MobileValidLength]
CHECK (LEN([mobile])<=30)
GO
ALTER TABLE StagingTable
WITH CHECK ADD CONSTRAINT [StagingTable$InternalExternalValid]
CHECK ([Internal/External] IN ('Internal','External'))
GO
--etc...

Answer 3

You need to concatenate the expressions together. I agree with #PinnyM that a where clause is easier for full table validation. However, the next question will be how to identify which rows fail which tests. I'll wait for you to ask that question before answering it (ask it as a separate question and not as an edit to this one).
To create the where clause, something like this:
declare #WhereClause nvarchar(max);
select #WhereClause = (select CustomValidation+' and '
from Validations v
for xml path ('')
) + '1=1'
select #WhereClause = replace(replace(#WhereClause, '<', '<'), '>', '>'))
This strange construct, with the for xml path('') and the double select, is the most convenient way to concatenate values in SQL Server.
Also, put together your query before doing the sp_executesql call. It gives you more flexibilty:
declare #sql nvarchar(max);
select #sql = '
select #passed = count(*)
from '+#StagingTableName+'
where '+#WhereClause
That is the number that pass all validation tests. The where clause for the fails is:
declare #WhereClause nvarchar(max);
select #WhereClause = (select 'not '+CustomValidation+' or '
from Validations v
for xml path ('')
) + '1=0'