SQL如果select語句不返回任何行，則執行替代選擇語句

Question

基本上，什麼syntex將允許我實現標題語句？

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

這樣無論從語句2或3 的sql返回結果我找了一個辦法做到這一點，但沒有我發現看似很遠，如果要求準確地解決。

Answer 1

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

Answer 2

在這裏你去...

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

Answer 3

對不起，缺乏反饋。辦公室裏的其他人對此感興趣，想出了這個：

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 

這就是我所需要的。