Simplified Order Of Operations

I recently learned that when combining multiple operators in a SQL expression, AND has a higher precedence than OR but & has the same precedence as |. I expected the precedence rules for the logical operators to be consistent with the bitwise operators.

Even Stephen Sondheim seemed to struggle with this.

AND is Always Evaluated Before OR

SELECT'TRUE'WHERE(1=1)OR(1=1)AND(1=0)-- returns TRUE 
SELECT'TRUE'WHERE(1=0)AND(1=1)OR(1=1)-- returns TRUE

& and | are Evaluated Left To Right

SELECT1|1&0-- returns 0 
SELECT0&1|1-- returns 1

Here Are The Official Docs

Here what Microsoft says about SQL Server’s Operator Precedence.

1. ~ (Bitwise NOT)
2. * (Multiply), / (Division), % (Modulo)
3. + (Positive), – (Negative), + (Add), (+ Concatenate), – (Subtract), & (Bitwise AND), ^ (Bitwise Exclusive OR), | (Bitwise OR)
4. =, >, =, <>, !=, !>, !
5. NOT
6. AND
7. ALL, ANY, BETWEEN, IN, LIKE, OR, SOME
8. = (Assignment)

Practical Subset

I have a book on my shelf called Practical C Programming published by O’Reilly (the cow book) by Steve Oualline. I still love it today because although I don’t code in C any longer, the book remains a great example of good technical writing.

That book has some relevance to SQL today. Instead of memorizing the full list of operators and their precedence, Steve gives a practical subset:

1. * (Multiply), / (Division)
2. + (Add), – (Subtract)

Put parentheses around everything else.