T-SQL - Operators Precedence

T-SQL Operators Precedence

Operator precedence (order of operations) is a collection of rules that reflect conventions about which procedures to perform first in order to evaluate a given expression.

For example, multiplication has higher precedence than addition. Thus, the expression 1 + 2 × 3 is interpreted to have the value 1 + (2 × 3) = 7, and not (1 + 2) × 3 = 9. When exponent is used in the expression, it has precedence over both addition and multiplication. Thus 3 + 5² = 28 and 3 × 5² = 75.

Example:

Consider the following expressions:

--evaluates 5 * 2 first
Result1 = 15 - 5 * 2;

--above expression is equivalent to
Result2 = 15 - (5 * 2);

--forcing compiler to evaluate 15 - 5 first
Result3 = (15 - 5) * 2;

Now, Consider a database table called Sample with the following records:

The above discussed can be applied on the table Sample. Consider the example below:

SELECT *, 
  Var1 - Var2 * 2 AS Result1,
  Var1 - (Var2 * 2) AS Result2,
  (Var1 - Var2) * 2 AS Result3 
FROM Sample;

The above query will produce following result:

T-SQL Operators Precedence Table

The following table lists the precedence of T-SQL operators. Operators are listed top to bottom, in descending precedence. Operators with higher precedence are evaluated before operators with relatively lower precedence.