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)
| Operator/Element | Associativity | Description |
|---|---|---|
| :: | left | PostgreSQL-style typecast |
| [ ] | left | array element selection |
| . | left | table/column name separator |
| - | right | unary minus |
| ^ | left | exponentiation |
| * / % | left | multiplication, division, modulo |
| + - | left | addition, subtraction |
| IS | test for TRUE, FALSE, UNKNOWN, NULL | |
| ISNULL | test for NULL | |
| NOTNULL | test for NOT NULL | |
| (any other) | left | all other native and user-defined operators |
| IN | set membership | |
| BETWEEN | containment | |
| OVERLAPS | time interval overlap | |
| LIKE ILIKE | string pattern matching | |
| < > | less than, greater than | |
| = | right | equality, assignment |
| NOT | right | logical negation |
| AND | left | logical conjunction |
| OR | left | logical 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.