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7.16.5 ALL

expression operator ALL (subquery)

The right-hand side is a parenthesized subquery, which must return exactly one column. The left-hand expression is evaluated and compared to each row of the subquery result using the given operator, which must yield a Boolean result. The result of ALL is “true” if all rows yield true (including the special case where the subquery returns no rows). The result is “false” if any false result is found. The result is NULL if the comparison does not return false for any row, and it returns NULL for at least one row.

NOT IN is equivalent to <> ALL.

As with EXISTS, it's unwise to assume that the subquery will be evaluated completely.

row_constructor operator ALL (subquery)

The left-hand side of this form of ALL is a row constructor, as described in section 2.2.11 Row Constructors. The right-hand side is a parenthesized subquery, which must return exactly as many columns as there are expressions in the left-hand row. The left-hand expressions are evaluated and compared row-wise to each row of the subquery result, using the given operator. The result of ALL is “true” if the comparison returns true for all subquery rows (including the special case where the subquery returns no rows). The result is “false” if the comparison returns false for any subquery row. The result is NULL if the comparison does not return false for any subquery row, and it returns NULL for at least one row.

See section 7.17.5 Row-wise Comparison for details about the meaning of a row-wise comparison.