Oracle in a Nutshell

Operators

Oracle supports the following standard operators:

• Arithmetic: + - * /

• Concatenation: ||

• Set operators, which work on groups of rows:

  UNION

  All rows selected by either query

  UNION ALL

  All rows selected by either query including duplicates

  INTERSECT

  All distinct rows selected by both queries

  MINUS

  All distinct rows selected by the first query but not the second

• User-defined operators: You can create your own special-purpose operators with the CREATE OPERATOR statement. New with Oracle9i.

Operators are evaluated according to the precedence level of the operator, where operators with precedence level 1 are evaluated first. Table B-1 lists the precedence levels of operators and conditions. All operators with the same precedence are evaluated left to right within an expression. Oracle will evaluate all operators within a set of parentheses first.

Table B-1. Precedence levels for operators and conditions

Precedence	Operator/condition
1	+ (positive), - (negative), PRIOR
2	*, /
3	+ (addition), - (subtraction), || (concatenation)
4	=, != (not equals), <, >, <=, >=
5	IS [NOT] NULL, [NOT] LIKE, [NOT] BETWEEN, [NOT] IN, EXISTS, IS [NOT] OF type
6	NOT
7	AND
8	OR

All set and user-defined operators have equal precedence and are evaluated from left to right after the expressions used in the operations have been evaluated.