SQL:通过将两个列映射到彼此来更新表。

I have the following two tables:

我有以下两张表:

        Table A
+-------------------+
|___User___|__Value_|
|    3     |  a     |
|    4     |  b     |
|    5     |  c     |
|____6_____|__d_____|



        Table B
+-------------------+
|___User___|__Value_|
|    1     |        |
|    4     |        |
|    5     |        |
|____9_____|________|

My job is to take user from Table A (and their correspondings value) and then map it to Table B and insert those values in there. So from the above example Table B should look like this after running the script:

我的工作是从表A(及其对应值)获取用户，然后将其映射到表B并将这些值插入其中。因此，从上面的例子来看，运行脚本后，表B应该是这样的:

        Table B
+-------------------+
|___User___|__Value_|
|    1     |        |
|    4     |  b     |
|    5     |  c     |
|____9_____|________|

My question is how can I construct an SQL query that will do this for me in an efficient way, if Table A contains 300,000 + entries and Table B contains 70,000 entries?

我的问题是，如果表A包含30万多个条目，而表B包含7万个条目，那么我如何构建一个SQL查询，以一种有效的方式实现这一点?

NOTES: In Table A the User field is not unique and neither is the Value field. However in Table B, both the User and Value fields are unique and should not appear more than once. Neither are primary keys for either tables.

注意:在表A中，用户字段不是唯一的，值字段也不是唯一的。然而，在表B中，用户和值字段都是惟一的，不应该出现多次。两个表的主键都不是。

3 个解决方案

#1

Could be this

可能是这

update table_b as b 
inner join table_a as a on a.User = b.User
set b.value = a.value

3 个解决方案

#1

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