SQL Select with multiple AND and OR's

Question

I'm sitting with a logic issues and I'm just confusing myself more and more.

Example table

ID | CustID | Task | Confirmed | Cancelled | Completed

1 | 20 | text | 1 | 0 | 0
2 | 20 | text | 1 | 1 | 0
3 | 20 | text | 1 | 0 | 1
4 | 17 | text | 0 | 1 | 0
5 | 17 | text | 1 | 0 | 0
6 | 20 | text | 1 | NULL | NULL
7 | 20 | text | 0 | 1 | NULL

I wish to select all tasks for custID = 20 and are confirmed=1. If the task is cancelled=1 or completed=1, do not return the record.

In this case, returned rows would be 1 and 6.

My query thus far is

SELECT *
FROM table1
WHERE    
 (CustID = 20 AND Confirmed = 1 AND Cancelled <> 1 AND Completed <> 1) OR
 (CustID = 20 AND Confirmed = 1 AND Cancelled = 1 AND Completed <> 1) OR
 (CustID = 20 AND Confirmed = 1 AND Cancelled <> 1 AND Completed = 1)

Any help would be greatly appreciated.

Answer 1

You can simplify that to:

SELECT * FROM table1
WHERE CustID = 20
  AND Confirmed = 1
  AND (Cancelled <> 1 OR Cancelled IS NULL)
  AND (Completed <> 1 OR Completed IS NULL)

You have to be careful (and very explicit) when comparing real values with NULLs, since equalities and inequalities both exclude them.

Answer 2

SELECT *
FROM table1
WHERE    
    CustID = 20 AND Confirmed = 1 AND NOT (Cancelled = 1 OR Completed = 1)