SQL Update，随时更新行。(SQL Update that Updates rows as it goes. So nothing is used Twice.)

 这个很难问，但我试图搜索，找不到一个例子。 
 
 我有两个表：对于第一个表“TableA”中的每一行，第二个表“TableB”中应该有一个匹配的行。 “TableA”将有一个外键，指向它在“TableB”中的匹配记录。 
 
 我需要更新“TableA”并根据某些标准填充此外键。问题是“TableB”中的多个记录可以匹配，但我不想使用“TableB”中的任何记录不止一次。 
 
 **因此，一旦我匹配第二个表中的一个记录，我就再也不想使用它了。 
 
 我做了这项工作，一次循环“TableA”一条记录，进行更新，并在我的标准中确保我不使用“TableB”中的记录，如果它已在“TableA”中引用。 
 
 但是，这很慢。 
 有没有办法在单个更新语句中执行此操作？ 让我知道如果你需要一个例子，我可能会假装一些东西。 

this one is hard to ask, but I tried to search and couldn't find an example. 
 
I have two tables: For every row in the first table "TableA", there should be a matching row in the second table "TableB". The "TableA" will have a foreign key that points to it's matching record in "TableB".
 
I need to update "TableA" and populate this foreign key, based on certain criteria.. The problem is more than one record in the "TableB" could match, but I don't want to use any of the records in "TableB" more than once. 
 
**So once I've matched one of the records in the second table I never want to use it again. 
 
I made this work, by looping "TableA" one record at a time, making my update, and making sure in my criteria that I don't use a record from "TableB" if it is already referenced in "TableA". 
 
However, THIS IS SLOW.
 Is there some way to do this in a single update statement? Let me know if you need an example, I can probably fake something. 

原文：https://stackoverflow.com/questions/35873002