A logical expression or relational expression returns TRUE, FALSE, or UNKNOWN. The general patterns are:
expression comparison_operator [any | all] expression
expression [not] in expression
[not]exists expression
expression [not] between expression and expression
expression [not] like "match_string" [escape "escape_character "]
not expression like "match_string" [escape "escape_character "]
expression is [not] null
not logical_expression
logical_expression {and | or} logical_expression
