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。