The IN and NOT IN operators in PostgreSQL are used to check whether a value is present in a list of values or not. The left-hand side operand must be of type text, smallint, integer, bigint, real, double precision, or an array of these types. The right-hand side operand can be of any type.If the left-hand side operand is NULL, the result of the IN operator is also NULL. If the right-hand side operand is an empty array, the result is always false.The PostgreSQL IN and NOT IN operators are used to determine whether a value is present in a list of values. The PostgreSQL IN operator is used to compare a value against a list of values, and return true if the value is present in the list. The PostgreSQL NOT IN operator is used to compare a value against a list of values, and return true if the value is not present in the list.The PostgreSQL IN operator is used to check whether a value is in a list of values. The list of values can be literal values, subquery, or expression. If the list contains null values, the result of the IN operator is unknown.The NOT IN operator is the opposite of the IN operator. It returns true if the value is not in the list of values.