What points to be kept in mind while using conditional operator i.e. AND, NOT & OR operator

AND operator: does not hurt the performance of the database engine the reason is that it in fact reduces the result from the result set.

OR operator : When Index is used with the OR operator then all the column used/referenced by the OR operator in the where clause must include in an index or none of the indexes are used.

NOT operator: It hurts the performance of the database engine the reason is that the query optimizer which optimizes the query is not able to use index for the where clause when ever a NOT operator is used/specified in the where clause of the query