AP 29 - Use parentheses when mixing ANDs with ORs

Severity

Type

Problem

There are a few important rules about how operators and conditions precede each other. The most important rule for conditions is that AND comes before OR.

Don’t make complicated expressions that require the reader to know the rules perfectly. Use spaces and parentheses to make the logic clear.

SELECT c1 
  FROM table1 
 WHERE x=1
    OR z=5
   AND y=2

Solution

Use parentheses when mixing ANDs with ORs to improve readability

SELECT c1 
  FROM table1 
WHERE x=1
OR(z=5
AND y=2)

Please note it’s very different to:

SELECT c1 
  FROM table1 
 WHERE(   x=1
       OR z=5
      )
   AND y=2

and in the above case the logic can’t be expressed without brackets.

Legitimate use of the anti pattern

None