$(2$ Marks$)$ The UNIQUE operator evaluates to true if there are no duplicate tuples in the result of

some subquery. This operator does not exist in Postgres. The following query returns each

employee who has exactly one dependent. Rewrite this query so it will run in Postgres. Use a

subquery.

SELECT $*$

FROM employee c

WHERE UNIQUE

$($SELECT essn

FROM dependent d

INNER JOIN employee o

ON o$.$ssn$=$ d$.$essn

WHERE o$.$ssn$=$c$.$ssn$)$;