IN Operator

The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below does not delete the rows in which the ename column is null:

DELETE FROM emp WHERE ename IN (NULL, ’KING’, ’FORD’);

Moreover, the expressions of the form

value NOT IN set

yield FALSE when  the set contains a null. For illustration, instead of deleting the rows in which the ename column is not null and not ’KING’, the statement below deletes no rows:


DELETE FROM emp WHERE ename NOT IN (NULL, ’KING’);


Concatenation Operator

The Double vertical bars (||) serve as the concatenation operator that appends one string to another. For illustration, the expression

’suit’ || ’case’

returns the value as shown below:

’suitcase’

If both the operands have datatype CHAR, the concatenation operator returns a CHAR value. Or else, it returns a VARCHAR2 value.