Question

我正在尝试使用另一个表中的列更新表。我不想查看联接，我想改变表格。

然而，这是假的：

UPDATE
a_dataset
SET
a_dataset.lang_flag = b_dataset.language
FROM
a_dataset
INNER JOIN
b_dataset
ON
a_dataset.ID = b_dataset.ID

但是，我一直收到语法错误，找不到我错过的内容？

Answer 1

I am guessing that you mean to update your records when you say alter the table. If so, you can simply rewrite your update statement with join like this:

UPDATE a_dataset a
JOIN b_dataset b ON a.ID = b.ID
SET a.lang_flag = b.[LANGUAGE]

Answer 2

As Uueerdo and myself said: Starting table names with numbers is a bad[TM] idea. The same is for letters, which you now chose to use. a is no better than 1 in this regard. Also calling tables just "dataset" isn't really helpful either. What is the table storing? Users? Then call it users. Articles on a news web site? Then call it articles. And so on. Everything in a database is dataset, no need to tell that anyone.

I guess you're new to SQL, am I right? Because another issue is: Unless you're going to drop table b_dataset after this command, you're probably doing something you're not supposed to do in relational data bases. The whole idea is to store all data only once. If you can automagically copy the column from b to a, then you could also select join if from a and b when you need it instead of copying it.

For learning SQL (or anything else), Stack Overflow is probably a bad place (it's good for asking questions in the process, though), so I recommend that you go get someone who has some experience in SQL to teach you, or get some book / tutorial on SQL. From first glance, this seems to be a good on-line book: http://sql.learncodethehardway.org/ - but I didn't read it.

使用JOIN的MSQL alter table

2 个答案: