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1.4. Lexical Precedence

The precedence and associativity of the operators is hard-wired into the parser. Most operators have the same precedence and are left-associative. This may lead to non-intuitive behavior; for example the Boolean operators < and > have a different precedence than the Boolean operators <= and >=. Also, you will sometimes need to add parentheses when using combinations of binary and unary operators. For instance

SELECT 5 ! - 6;

will be parsed as

SELECT 5 ! (- 6);

because the parser has no idea -- until it is too late -- that ! is defined as a postfix operator, not an infix one. To get the desired behavior in this case, you must write

SELECT (5 !) - 6;

This is the price one pays for extensibility.

Table 1-1. Operator Precedence (decreasing)

::leftPostgreSQL-style typecast
[ ]leftarray element selection
.lefttable/column name separator
-rightunary minus
* / %leftmultiplication, division, modulo
+ -leftaddition, subtraction
ISNULL test for NULL
(any other)leftall other native and user-defined operators
IN set membership
BETWEEN containment
OVERLAPS time interval overlap
LIKE ILIKE string pattern matching
< > less than, greater than
=rightequality, assignment
NOTrightlogical negation
ANDleftlogical conjunction
ORleftlogical disjunction

Note that the operator precedence rules also apply to user-defined operators that have the same names as the built-in operators mentioned above. For example, if you define a "+" operator for some custom data type it will have the same precedence as the built-in "+" operator, no matter what yours does.