Precedence

Precedence is the order in which Oracle evaluates different operators in the same expression. When evaluating an expression containing multiple operators, Oracle evaluates operators with higher precedence before evaluating those with lower precedence. Oracle evaluates operators with equal precedence from left to right within an expression.

Table 3-1 lists the levels of precedence among SQL operators from high to low. Operators listed on the same line have the same precedence.

Table 3-1 SQL Operator Precedence  

Operator	Operation
+, -	identity, negation
*, /	multiplication, division
+, -, ||	addition, subtraction, concatenation
=, !=, <, >, <=, >=, IS NULL, LIKE, BETWEEN, IN	comparison
NOT	exponentiation, logical negation
AND	conjunction
OR	disjunction

Example

In the following expression, multiplication has a higher precedence than addition, so Oracle first multiplies 2 by 3 and then adds the result to 1.

1+2*3 

You can use parentheses in an expression to override operator precedence. Oracle evaluates expressions inside parentheses before evaluating those outside.

SQL also supports set operators (UNION, UNION ALL, INTERSECT, and MINUS), which combine sets of rows returned by queries, rather than individual data items. All set operators have equal precedence.