mysql的一条if语句，不知道怎么移植到pgsql中
select sum(if(r.receive_type=1,r.money,0)) from receive_money r, salesbook s where r.id = s.id and r.id=51

谢谢！

------解决方案--------------------
select sum(case when r.id=1 then r.value else 0 end) from receive r, sales s where r.book_id = s.id and s.id=10;