MySQL 如何只加入一列？
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How to join only one column?
提问by Kevin Grace
SELECT * FROM table1
LEFT JOIN table2
ON table1.id = table2.table1_id
WHERE table1.id = 1
I need to join only one column from table 2, say first_name. How can I do that?
我只需要加入表 2 中的一列，比如 first_name。我怎样才能做到这一点？
回答by NullUserException
Assuming that you mean "select one column from table 2":
假设您的意思是“从表 2 中选择一列”：
SELECT table1.*, table2.first_name
FROM table1
LEFT JOIN table2
...
回答by MTK
The accepted answer is the correct answer but I have encountered a strange error when the tables are in two different databases:
接受的答案是正确的答案，但是当表位于两个不同的数据库中时，我遇到了一个奇怪的错误：
Assuming that table1 is in database1 and table2 is in database2. Initially I have tried this:
假设 table1 在 database1 中，table2 在 database2 中。最初我试过这个：
SELECT *, database2.table2.first_name FROM table1
LEFT JOIN database2.table2
ON database1.table1.id = database2.table2.table1_id
WHERE table1.id = 1
The strange thing is that if I try this query from PHP PDO there were no errors but the result contained all columns from database2.table2 (expected only first_name column).
奇怪的是，如果我从 PHP PDO 尝试这个查询，没有错误，但结果包含来自 database2.table2 的所有列（预计只有 first_name 列）。
But if I have tried the same query from phpmyadmin got a sintax error:
但是，如果我从 phpmyadmin 尝试了相同的查询，则会出现 sintax 错误：
Table 'database2.table1' doesn't exist
表“database2.table1”不存在
So, for solve that, then all databases need to be specified implicitly like this:
因此，为了解决这个问题，所有数据库都需要像这样隐式指定：
SELECT database1.table1.*, database2.table2.first_name FROM database1.table1
LEFT JOIN database2.table2
ON database1.table1.id = database2.table2.table1_id
WHERE database1.table1.id = 1
回答by davecoulter
Do you mean in addition to your already stated query:
除了您已经陈述的查询之外，您的意思是：
SELECT * FROM table1
LEFT JOIN table2
ON table1.id = table2.table1_id
WHERE table1.id = 1 and table1.first_name = table2.first_name
回答by Jacob Hamfeldt Kold
Take your original code and substitute * with table1.*, table2.YourChosenColumn
获取您的原始代码并将 * 替换为 table1.*, table2.YourChosenColumn
SELECT table1.*, table2.YourChosenColumn
FROM table1 LEFT JOIN table2
ON table1.id = table2.table1_id
WHERE table1.id = 1
