SQL if select statement returns no rows then perform alternative select statement

Basically, what syntex would allow me to achieve the title statement?

If (select statement 1) returns 0 rows THEN (select statement 2) else (select statement 3)

So that the sql returns results from either statement 2 or 3 I've looked for a way to do t开发者_StackOverflow中文版his but nothing I've found so far seems to exactly address the if requirements.

IF EXISTS (SELECT field FROM table)
BEGIN
SELECT field FROM table2
END
ELSE
BEGIN
SELECT field FROM table3
END

Here you go...

IF ((select count(*) from table1)= 0)
BEGIN
Select * from table2
END
ELSE
BEGIN
SELECT * from table3
END

Sorry for the lack of feedback. Someone else in the office took an interest and came up with this:

select * from (
        select *
              , (SELECT Count(*) 
                   FROM users 
                  WHERE version_replace = 59 AND moderated = 1) AS Counter 
          FROM users WHERE version_replace = 59 AND moderated in (0,1)
     ) AS y
where Counter = 0 and Moderated = 0
   or Counter > 0 and Moderated = 1
ORDER By ID DESC

Which does what I need.