About SQL Operators

Operators manipulate individual data items called operands or arguments. Operators are represented by special characters or by keywords. For example, the multiplication operator is represented by an asterisk (*).

Unary and Binary Operators

The two general classes of operators are:

• unary: A unary operator operates on only one operand. A unary operator typically appears with its operand in this format:

  operator operand
  
  

• binary: A binary operator operates on two operands. A binary operator appears with its operands in this format:

  operand1 operator operand2
  
  

Other operators with special formats accept more than two operands. If an operator is given a null operand, the result is always null. The only operator that does not follow this rule is concatenation (||).

Operator 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
+, - (as unary operators), PRIOR	identity, negation, location in hierarchy
*, /	multiplication, division
+, - (as binary operators), ||	addition, subtraction, concatenation
SQL conditions are evaluated after SQL operators	See "Condition Precedence"

Precedence 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.