Logical operators: and, or, not
These operators implement Boolean conjunction, disjunction, and negation, respectively. AND and OR take two Boolean operands each, while NOT takes a single operand. All return Boolean values.
For AND and OR, both operands may be evaluated even if one operand is undefined, particularly in queries against multiple databases. For example, the clause:
WHERE QUANTITY <> 0 AND TOTALCOST / QUANTITY > 50
may result in an error for rows where QUANTITY = 0.

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