NOT statement in where Clause in SQL Server Slow-CodePudding

I have this query , where the results are as expected but the query is really slow. The below is just an example

SELECT ispending, isviewable, iscomparable, ID
FROM tableA
WHERE
    name = 'Karen' 
    AND NOT ((ispending = 'F' AND isviewable = '0') OR
             (ispending = 'T' AND iscomparable = '0') OR
             (ispending = 'T' AND iscomparable IS NULL AND isviewable = '0') OR
             (ispending IS NULL AND iscomparable = '0'))

How to achieve the same result but not using the 'NOT' statement in the where clause?

I tried changing the not to be within the clause

WHERE (ispending != 'F' AND isviewable != '0') OR
      (ispending != 'T' AND iscomparable != '0') OR
      (ispending != 'T' AND iscomparable IS NOT NULL AND isviewable != '0') OR
      (ispending IS NOT NULL AND iscomparable !='0')

but the expected results are different.

CodePudding user response：

You're second code block is quite close. De Morgan's law guides in trying to switch operands on boolean operations.

The code is correct to switch = with != (the negation of the =). But you will also need to negate conjunctions/disjunctions. In essence: AND becomes OR and vice versa.

WHERE (ispending != 'F' OR isviewable != '0') AND
      (ispending != 'T' OR iscomparable != '0') AND
      (ispending != 'T' OR iscomparable IS NOT NULL OR isviewable != '0') AND
      (ispending IS NOT NULL OR iscomparable != '0')

Now we have the logical equivalent.