SQL Server 用一张表的数据更新另一张表的数据（转载）

文章一：SQL Server中如何基于一个表的数据更新另一个表的对应数据的SQL语句脚本

https://codedefault.com/2017/sql-server-update-from-a-select

方式一 INNER JOIN

UPDATE
    Table_A
SET
    Table_A.col1 = Table_B.col1,
    Table_A.col2 = Table_B.col2
FROM
    Some_Table AS Table_A
    INNER JOIN Other_Table AS Table_B
        ON Table_A.id = Table_B.id
WHERE
    Table_A.col3 = 'cool'

方式二 使用MERGE关键字

MERGE INTO YourTable T
   USING other_table S
      ON T.id = S.id
         AND S.tsql = 'cool'
WHEN MATCHED THEN
   UPDATE
      SET col1 = S.col1,
          col2 = S.col2;

或者

MERGE INTO YourTable T
   USING (
          SELECT id, col1, col2
            FROM other_table
           WHERE tsql = 'cool'
         ) S
      ON T.id = S.id
WHEN MATCHED THEN
   UPDATE
      SET col1 = S.col1,
          col2 = S.col2;

注： SQL Server 2008 或者以上版本才支持MERGE关键字

方式三 使用CTE

;WITH CTE
     AS (SELECT T1.Col1,
                T2.Col1 AS _Col1,
                T1.Col2,
                T2.Col2 AS _Col2
         FROM   T1
                JOIN T2
                  ON T1.id = T2.id
         /*Where clause added to exclude rows that are the same in both tables
           Handles NULL values correctly*/
         WHERE EXISTS(SELECT T1.Col1,
                             T1.Col2
                       EXCEPT
                       SELECT T2.Col1,
                              T2.Col2))
UPDATE CTE
SET    Col1 = _Col1,
       Col2 = _Col2

方式四 使用EXISTS

UPDATE suppliers
SET supplier_name = (SELECT customers.name
                     FROM customers
                     WHERE customers.customer_id = suppliers.supplier_id)
WHERE EXISTS (SELECT customers.name
              FROM customers
              WHERE customers.customer_id = suppliers.supplier_id);

文章二：SQL 用一个表的数据更新另一张表

https://blog.51cto.com/alun51cto/2392062?source=dra

用表B的数据（B1列,B2）更新表A的A1,A2列

SQL Server:

update A SET A.A1 = b.B1,A.A2=B.A2 FROM A ,B WHERE  A.ID1 = B.ID1 and A.ID2 = B.ID2;

Access:

update A, B  set A.A1 = B.B1,A.A2=B.B2 where A.ID1 = B.ID1 and A.ID2 = B.ID2;

--或

update A INNER JOIN B ON A.ID1 = B.ID1 AND A.ID2= B.ID2 SET A.A1 = B.B1,A.A2=B.B2;

通过一条ＳＱＬ语句一次更新多条数据．ＳＱＬ语句写法略有不同，如下：

方法一:

Update T1
set dc=(select dc1 from t2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.AID in (
    SELECT AID FROM T1
    INNER JOIN T2 ON t1.A=T2.A1 AND T1.B=T2.B1
)

注：在我标我红色的in地方如果把'in'换成'='将出错，但在下面的Ｂ种写法里就可以换成'=',变成Ｃ方法写法.

方法二：

Update T1
set dc=(select dc1 from t2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.AID in (
    SELECT T1.AID FROM T2
    WHERE t1.A=T2.A1 AND T1.B=T2.B1
)

方法三：

Update T1
set dc=(select dc1 from t2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.AID = (
    SELECT T1.AID FROM T2
    WHERE t1.A=T2.A1 AND T1.B=T2.B1
)

方法四：

Update T1
set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.A = (
    SELECT T1.A FROM T2
    WHERE T1.A=T2.A1 AND T1.B=T2.B1
)

方法五：

Update T1
set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.A = (
    SELECT T2.A1 FROM T2
    WHERE T1.A=T2.A1 AND T1.B=T2.B1
)

方法六:　

Update T1
set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.A in (
    SELECT T2.A1 FROM T2
    WHERE T1.A=T2.A1 AND T1.B=T2.B1
)

注：如果在上面方法改写成如下的写法将会出错。

Update T1
set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1)
WHERE T1.A in (
    SELECT T1.A FROM T1
    INNER JOIN T2 ON t1.A=T2.A1 AND T1.B=T2.B1
)

此种方法将会更新掉所有符合T1.A in ()这个条件的数据,所以是不正确的, 所以不能这样写。

方法七：

Update T1
set dc=(select dc1 from T2 where T1.A=T2.A1 AND T1.B=T2.B1 AND T1.DC=T2.DC1)
FROM T1, T2
WHERE  T1.A=T2.A1 AND T1.B=T2.B1

方法八：

Update T1
set T1.dc=T2.dc1
FROM T1
INNER JOIN T2 ON T1.A=T2.A1 AND T1.B=T2.B1
WHERE t1.A=T2.A1 AND T1.B=T2.B1

方法九：

Update T1
set T1.dc=T2.dc1
FROM T1, T2
WHERE  T1.A=T2.A1 AND T1.B=T2.B1

请特别注意以上方法中我用红色标记上的代码写法。

总节：虽然是一条简单的更新语名但也有多种写法，且每种写法各有优缺点。

大家是否还有更简单的写法或者更容易理解的写法？如果有请提出来一起讨论，谢谢！

说明测试环境：以上代码在ＭＳＳＱＬ2005中验证是可行的．

　　注：此处我用灰色标记的部分可以去掉。