在 SQL 中找到两个集合的最紧凑和最有效的方法是什么？ [复制]

Question

举个简单的例子，假设我有两个表

  T1                      T2
=======                 =======
  Val                     Val
=======                 =======
   1                       1
   2                       3
   4                       4
   5                       5
                           6

我想要的结果集是

2
3
6

因为这些是包含在其中一个而不是另一个中的数字。我知道它可以用类似的东西来完成

WITH cte1 (Val) AS (
    SELECT Val
    FROM T1
    LEFT JOIN T2
    ON T1.Val = T2.Val
    WHERE Val IS NOT NULL
),
cte2 (Val) AS (
    SELECT Val
    FROM T2
    LEFT JOIN T1
    ON T1.Val = T2.Val
    WHERE Val IS NOT NULL
)
SELECT *
FROM cte1
UNION WITH cte2

但是有没有更紧凑和/或更有效的方法来做到这一点？

Answer 1

使用 or 子句应该可以使用完全外连接。

SELECT isnull(t1.Val,t2.Val) [Val]
    FROM T1
    FULL OUTER JOIN T2
    ON T1.Val = T2.Val
WHERE T1.Val is null OR T2.Val is null

Answer 2

我会这样做：

select t1.* 
from t1
where not exists (select 1 from t2 where t2.val = t1.val)
union all
select t2.* 
from t2
where not exists (select 1 from t1 where t2.val = t1.val);