</code>AnINconditionalexpressionreturnstrueifthe//operand// is found from result of the //subquery//orifitsinthespecificiedcommaseparated//value list//, hence the IN expression is always false if the result of the subqueryisempty.When//value list// is being used there must be at least one element in that list.<code>FROMC1WHEREC1.col1IN(FROMC2(col1));FROMUserWHEREUser.idIN(1,3,4,5)</code>ThekeywordINisanaliasfor=ANY.Thus,thesetwostatementsareequal:<code>FROMC1WHEREC1.col1=ANY(FROMC2(col1));FROMC1WHEREC1.col1IN(FROMC2(col1));</code>