t-sql中有循环吗？用它们是个好主意？-arethereloopsint-sql?isusingthemagoodidea?

5  

No loop necesary for what you want, it seems that you only need IN:

没有循环需要你想要的东西,似乎你只需要IN:

SELECT *
FROM TableX
WHERE CustomerID IN (SELECT CustomerID FROM TableT)

If you need to update TableX with some mark if exists on TableT, it should be:

如果你需要用TableT上的某个标记更新TableX,它应该是:

UPDATE TableX
SET Mark = 1
WHERE CustomerID IN (SELECT CustomerID FROM TableT)

If you need to update TableX with some value from TableT, it should be something like this:

如果您需要使用TableT中的某些值更新TableX,它应该是这样的:

UPDATE X
SET X.Column = T.Column
FROM TableX X
INNER JOIN TableT T
ON X.CustomerID = T.CustomerID 

3  

Looping is a red flag in SQL and is not usually needed. SQL is based on set theory. Understand JOINs and you will rarely need to iterate.

循环是SQL中的一个红旗,通常不需要。 SQL基于集合论。理解JOIN,你很少需要迭代。

So, in your case, no, looping is neither necessary nor a good idea.

所以,在你的情况下,不,循环既不是必要的也不是一个好主意。