in in a in (b, c, d, ..., null), there is a NULL value inside the brackets inside the comparison, then the comparison value to see whether inside the other with the presence of a value equal to, if it returns true, otherwise return false.
in not in a not in (b, c, d, ..., null), if present brackets NULL, then always returns false.
exists in the associated query exists inside NULL if present, the internal query is not a query result, there exists at least one line does not meet the determination result set returned, thus returns false.
not exists not exists in the context of the query conditions inside if there is NULL, then the inner query is a query no results, in line with expectations determine not exists for no result set returned, so return true.
