在SQL中，如何通过查找列相等的所有行来更新表的每一行，然后将另一列设置为等于另一列

So basically this would be the psuedo code, but I don't know how to do this in SQL, please help.

所以基本上这将是伪代码，但我不知道如何在SQL中执行此操作，请帮忙。

for each row in table1{
    loop through each row in table 2 {
        if table1's row.column 1 = table2's row.column 2 for this row {
            set table1's row.col2 = table2's row.col2
        }
    }
}

Edit: Okay let me be more specific. We are basically switching from hibernate sequence as ids to using guids for the id column. I'm trying to update the foreign keys associated by making a temp of the previous foreign key column and then matching the temporary columns to update the actual columns.

编辑：好的，让我更具体一点。我们基本上从hibernate序列切换为id，使用guid作为id列。我正在尝试通过创建前一个外键列的临时更新相关的外键，然后匹配临时列以更新实际列。

suppose table one had id's and table two had a column for those ids to use as foreign keys. I wanna use the previous values in table 2 to match with the rows in table 1 and set the key values in table 2 to match the new guid of table 1.

假设表1有id，而表2有一列用于将这些id用作外键。我想使用表2中的先前值与表1中的行匹配，并设置表2中的键值以匹配表1的新guid。

so table 2 may have multiple rows of duplicate id's but table 1 will never have duplicates. If that makes any sense.

所以表2可能有多行重复的id，但表1永远不会有重复。如果那有意义的话。

2 个解决方案

#1

In SQL Server you can do something like:

在SQL Server中，您可以执行以下操作：

UPDATE Table_1
SET Column_2 = t2.Column_2
FROM Table_1 AS t1
INNER JOIN Table_2 AS t2 ON t2.Column_1 = t1.Column_1

or something like

或类似的东西

UPDATE Table_1
SET Column_2 = ( 
    SELECT t2.Column_2
    FROM Table_2 AS t2
    WHERE t2.Column_1 = Table_1.Column_1
)

Of course if you have multiple rows in Table_2, you will get an error....

当然，如果Table_2中有多行，您将收到错误....

#2

The basics of it is:

它的基础是：

UPDATE Table1 SET col2 =
     (select col2 FROM Table2 where Table2.column2 = Table1.column1)

But that may not do exactly what you need if there's not a 1-1 correspondence between rows in the two tables - and hence my current comment below your question:

但是，如果两个表中的行之间没有1-1对应关系，那么这可能无法完全满足您的要求 - 因此我当前的评论低于您的问题：

What should happen if there are more than one matching row in table 2? What should happen if there's no matching row?

如果表2中有多个匹配的行，会发生什么？如果没有匹配的行会发生什么？

#1