SQL CASE between values of the same table - sql

Question

I have the following #temp table :
SELECT *
FROM #temp
WHERE LinkingID = 1
------------------------------------------------------------------
|Condition_ID LinkingID Operator Variable1 Variable2 |
| 1 1 == 25 2 |
| 2 1 <> 3 7 |
| 3 1 == 4 4 |
------------------------------------------------------------------
I want to implement a CASE ( ??? ) that will check if Variable1 OPERATOR Variable2 is true, make the check for all rows and IF all rows are true then do something, else break off and abort.
I was thinking something like this ( I'm not sure how to express this in T-SQL so I use pseudolanguage ) :
CASE
WHEN Operator LIKE '=='
THEN IF Variable1 == Variable2 THEN TRUE
ELSE THEN FALSE
WHEN Operator LIKE '<>'
THEN IF Variable1 <> Variable2 THEN TRUE
ELSE THEN FALSE
FROM #temp
If the result of this is true for all rows, then do something, else do something else
In the scenario above :
Row1 would return FALSE
Row2 would return TRUE
Row3 would return TRUE
Hence the result is FALSE.

Answer 1

Accumulating comparison results over the whole table
Checking that the whole table returns true for all rows is best done to count false ones and check whether that number is greater equal to 0. If it's 0 then it means that all rows matched otherwise number indicates number of rows that failed
Mind the inverted comparison compared to Operator value to catch negatives:
declare #NonMatched int
select
#NonMatched = sum(
case
when [Operator] = '==' and Variable1 <> Variable2 then 1
when [Operator] = '<>' and Variable1 = Variable2 then 1
else 0
end
)
from #temp
where LinkingID = 1
if #NonMatched = 0
begin
-- execute your stored procedure or whatever else set of statements
end
Here's also a SQLFiddle that's based on upper code.

Answer 2

Im going to go out on a limb and guess you're trying to do something with all rows which the conditional variable 1 [operator] variable2 evaluates true. This could be selecting them, or deleting them - it makes no difference really.
I'll use a select as the example:
SELECT *
FROM #temp
WHERE LinkingID = 1
AND CASE Operator
WHEN '==' THEN Variable1 = Variable2
WHEN '<>' THEN Variable1 <> Variable2
END
The same where clause could be used if you wanted to delete these records.
EDIT To aggregate up this set and do something when all conditions for a particular LinkingID evaluate true, something like this will work:
IF EXISTS(
SELECT LinkingID FROM temp
WHERE LinkingID = 1
GROUP BY LinkingId
HAVING SUM(CASE
WHEN Operator = '==' AND Variable1 = Variable2 THEN 1
WHEN Operator = '<>' AND Variable1 <> Variable2 THEN 1
ELSE 0
END) = count(*)
)
BEGIN
-- Do something
END
Live example to play with here: http://www.sqlfiddle.com/#!6/26d72/6
In that example I have set up LinkingID=2 where all conditions are true. Change the LinkingId=1 to =2 to see the do something message.

Answer 3

I would write something like this:
SELECT
CASE WHEN NOT EXISTS
( SELECT *
FROM #temp
WHERE LinkingID = 1
AND NOT ( Operator = '==' AND Variable1 = Variable2
OR Operator = '<>' AND Variable1 <> Variable2
)
) THEN 'TRUE'
ELSE 'FALSE'
END AS Result ;