rowcount上的SQL条件联合

Question

我有一个返回小组列表的SQL函数。

我想通过联合来加入列表中的附加列表，但只有当第一个选择返回多于一行时。

喜欢的东西：

CREATE FUNCTION Teams() 
RETURNS TABLE 
AS 
RETURN 
(
    SELECT * FROM TABLE1 
    if @@rowcount>1  
    UNION 
    SELECT * FROM TABLE2 
    end if 
) 

Answer 1

如果我理解正确

CREATE FUNCTION Teams() 
RETURNS TABLE 
AS 
RETURN 
( 
    if (select COUNT(*) from TABLE2)>1 
    SELECT * FROM TABLE1 
    UNION 
    SELECT * FROM TABLE2 
    else 
    SELECT * FROM TABLE1 
) 

Answer 2

一种方式是做：

IF EXISTS(SELECT 1 FROM TABLE1) 
    SELECT * FROM TABLE1 
    UNION 
    SELECT * FROM TABLE2 
ELSE 
    SELECT * FROM TABLE1 

Answer 3

不漂亮，但这个应该工作：

CREATE FUNCTION Teams() 
RETURNS TABLE 
AS 
RETURN 
( 
    SELECT * FROM TABLE1 
    UNION 
    SELECT * FROM TABLE2 WHERE EXISTS (SELECT * FROM TABLE1) 
) 

如果从第一个表复杂的你可以把它放到CTE中：

CREATE FUNCTION Teams() 
RETURNS TABLE 
AS 
RETURN 
( 
    WITH Result AS 
    (
     SELECT * FROM TABLE1 WHERE ComplicatedConditions = 1 
) 
    SELECT * FROM Result 
    UNION 
    SELECT * FROM TABLE2 WHERE EXISTS (SELECT * FROM Result) 
)