Case statement to determine if I should union

Question

I currently want to do some sort of conditional union. Given the following example:

SELECT  age, name
FROM    users
UNION
SELECT  25 AS age, 'Betty' AS name

Say I wanted to only union the second statement if the count of 'users' was >=2 , otherwise do not union the two.

In summary I want to append a table with a row if the table only has 2 or more values.

Answer 1

You could use an ugly hack something like this, but I think Tim's answer is better:

SELECT  age, name
FROM    users
UNION ALL

SELECT  25, 'Betty'
WHERE (SELECT COUNT(*) FROM users) > 1;

Answer 2

If it's in a stored-procedure you could use If...Else:

IF (SELECT COUNT(*) FROM users) < 2
 BEGIN
  SELECT  age, name
  FROM    users
  END
ELSE
  SELECT  age, name
  FROM    users
  UNION ALL
  SELECT  25 AS age, 'Betty' AS name

Otherwise you could try something like this:

SELECT  age, name
  FROM    users
  UNION ALL
  SELECT  TOP 1 25 AS age, 'Betty' AS name
  FROM users
  WHERE (SELECT COUNT(*) FROM users) >= 2

Note that i've used UNION ALL since it doesn't seem that you want to eliminate duplicates.

Played around here: http://sqlfiddle.com/#!6/a7540/2323/0

Edit: Instead of my second approach i prefer Zohar's. So if you can use If....Else prefer that otherwise WHERE (SELECT COUNT(*) FROM users) > 1 without a table.