Operator precedence in WHERE in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does operator precedence mean in a SQL WHERE clause?

Operator precedence determines the order in which SQL evaluates conditions in the WHERE clause. Some operators are checked before others, affecting which rows are selected.

beginner

Which operator has higher precedence: AND or OR in a WHERE clause?

AND has higher precedence than OR. This means conditions joined by AND are evaluated before those joined by OR unless parentheses change the order.

beginner

How can you change the default operator precedence in a WHERE clause?

You can use parentheses () to group conditions and control the order of evaluation, overriding the default precedence rules.

intermediate

Given the WHERE clause: WHERE A = 1 OR B = 2 AND C = 3, which condition is evaluated first?

The condition B = 2 AND C = 3 is evaluated first because AND has higher precedence than OR.

beginner

Why is it important to understand operator precedence in SQL WHERE clauses?

Understanding operator precedence helps you write correct queries that return the expected results by ensuring conditions are evaluated in the intended order.

Which operator is evaluated first in a SQL WHERE clause without parentheses?

A NOT

B OR

C AND

D BETWEEN

NOT has the highest precedence, so it is evaluated before AND and OR.

In the condition WHERE A = 1 OR B = 2 AND C = 3, which part is evaluated first?

A B = 2 AND C = 3

B A = 1 OR B = 2

C A = 1 OR C = 3

D All conditions evaluated at the same time

AND has higher precedence than OR, so B = 2 AND C = 3 is evaluated first.

How do parentheses affect operator precedence in WHERE clauses?

A They have no effect

B They force evaluation of enclosed conditions first

C They lower the precedence of operators inside

D They only affect ORDER BY clauses

Parentheses force SQL to evaluate the conditions inside them before others, overriding default precedence.

Which of these is the correct order of operator precedence in WHERE clauses from highest to lowest?

A OR, AND, NOT

B AND, OR, NOT

C NOT, AND, OR

D AND, NOT, OR

NOT is evaluated first, then AND, then OR.

What happens if you mix AND and OR without parentheses in a WHERE clause?

A SQL throws an error

B Conditions are evaluated left to right regardless of operator

C OR conditions are evaluated before AND conditions

D AND conditions are evaluated before OR conditions

AND has higher precedence, so those conditions are evaluated before OR conditions.

Explain how operator precedence affects the evaluation of conditions in a SQL WHERE clause.

Think about which operators SQL checks first when filtering rows.

Describe how to use parentheses to control operator precedence in a WHERE clause and why it might be necessary.

Consider a query where AND and OR are mixed and the result is unexpected.