Question

in a Table there is a single attribute(column).it contains numbers.Some are repeated(2 or 3 and so on times) and some appears only one time.write as many queries to output all the numbers only once(apart from using distinct in SQL query).

Answer 1

It appears you don’t need the HAVING clause:

SELECT v1
FROM ztable
GROUP by v1
        ;

The HAVING clause will make things worse: it would only list the values that occur only once!