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# Operators

Operators are used to compose identifiers and literals into larger expressions. Operators can be logical operators , arithmetic operators, or comparison operators.

## Logical Operators

The logical operators are `NOT`, `AND`, and `OR`. These are in precedence order. These have the usual Boolean logic semantics. If a logical operator is applied to header fields or properties whose value is `NULL`, then the following rules apply:

• `AND`ing a `NULL` value with a `FALSE` value evaluates to `FALSE`; `AND`ing a `NULL` with a `TRUE` or `NULL` value evaluates to a NULL (or unknown) value.

• `OR`ing a `NULL` value with a `TRUE` value evaluates to `TRUE`; `OR`ing a `NULL` with a `FALSE` or a `NULL` value evaluates to a `NULL` (or unknown) value.

• Applying `NOT` to a `NULL` value evaluates to a `NULL` (or unknown) value.

## Arithmetic Operators

The arithmetic operators, in precedence order, are `+` and `-` (unary); `*` and `/`; and `+` and `-` (binary). These have the usual arithmetic semantics. Any arithmetic operator that is applied to one or more `NULL` values evaluates to a `NULL` value.

## Comparison Operators

The comparison operators can be loosely grouped into equality comparisons and range comparisons. The basic equality comparison operators, in precedence order, are `=`, `>`, `>=`, `<`, `<=`, and `<>`. These binary operators have to be applied to two values of the same type, else the expression will always evaluate to `FALSE`. If either value is `NULL`, then the result of the comparison is `NULL`. There are also the equality operators `IS NULL` and `IS NOT NULL` to compare ...

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