Removal of cursor which is processing bad data - sql

Question

How can we remove cursor in the following scenario:
DECLARE #Tablesq TABLE (numbercol INT)
INSERT INTO #Tablesq
SELECT 25 UNION all
SELECT -25 UNION all
SELECT 25 UNION all
SELECT 36
DECLARE #number INT
DECLARE sqrtcur CURSOR FOR SELECT numbercol FROM #tablesq
OPEN sqrtcur
FETCH NEXT FROM sqrtcur INTO #number
WHILE ##FETCH_STATUS = 0
BEGIN
BEGIN TRY
SELECT SQRT(#number)
END TRY
BEGIN CATCH
print ERROR_MESSAGE();
END CATCH
FETCH NEXT FROM sqrtcur INTO #number
END
CLOSE sqrtcur
DEALLOCATE sqrtcur
Here -25 value is causing the error and because of which I am forced to use the cursor. Can we do a set-based operation to achieve the same result?

Answer 1

SQL Server does not provide very good error handling within a SELECT statement. The one exception is for type conversion and the try_ functions -- but even that is relatively recently in the history of the database.
SQL is not alone in this. The standard just does not address this point.
The one thing you can do is use a case expression, if you understand the conditions when you will get an error:
select (case when numbercol >= 0 then sqrt(numbercol) end)
from tablesq;
SQL Server guarantees that the when conditions are evaluated in order, stopping at the first match, and the then is evaluated after then when. I should say "under almost all circumstances"; there are some optimizations made in aggregation queries that somewhat weaken that statement.
Many other databases have similar limitations. And in most of them, you can use a user-defined function that catches the exception. Alas, SQL Server does not allow try/catch blocks in UDFs, so this is not an option.

Answer 2

Are you looking for this:
SELECT SQRT(numbercol)
FROM #Tablesq
WHERE numbercol > 0;

Answer 3

You can do it this way :
DECLARE #tablesq TABLE (numbercol INT)
INSERT INTO #tablesq
SELECT 25 UNION all
SELECT -25 UNION all
SELECT 25 UNION all
SELECT 36;
DECLARE #number INT;
DECLARE sqrtcur CURSOR FOR SELECT numbercol FROM #tablesq;
DECLARE #TEST FLOAT;
OPEN sqrtcur;
FETCH NEXT FROM sqrtcur INTO #number;
WHILE ##FETCH_STATUS = 0
BEGIN
BEGIN TRY
SET #TEST = SQRT(#number);
SELECT SQRT(#number);
END TRY
BEGIN CATCH
print ERROR_MESSAGE();
END CATCH;
FETCH NEXT FROM sqrtcur INTO #number;
END;
CLOSE sqrtcur;
DEALLOCATE sqrtcur;