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2.1.6 Lexical Precedence

Table 2-1 shows the precedence and associativity of the operators in PostgreSQL. Most operators have the same precedence and are left-associative. The precedence and associativity of the operators is hard-wired into the parser. 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.

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.

When a schema-qualified operator name is used in the OPERATOR syntax, as for example in

SELECT 3 OPERATOR(pg_catalog.+) 4;

the OPERATOR construct is taken to have the default precedence shown in Table 2-1 for “any other” operator. This is true no matter which specific operator name appears inside OPERATOR().