I would like to know how to check the where clause if any of the line has a certain number. For example: If a select returns
1
2
3
4
and in the request clause 4 it returns the values, if it returns
1
2
3
and in request clause 4 it returns empty.
I do not know if it was clear, if there is doubt I rewrite the question. Thank you in advance.
If I understand correctly, I think that using the EXISTS clause does what you want. The query would be something like this:
SELECT numero FROM numeros WHERE EXISTS(SELECT numero FROM numeros WHERE numero = 4)
EXISTS returns true if the subquery returns some line.
If there is a number 4 in the EXISTS table, it returns true causing the query to return the numbers.
Otherwise EXISTS returns false and query will return zero rows
See working in SQLFiddle