从tb1到另一个表tb2的2列连接 [英] join of 2columns from tb1 to another table tb2

问题描述

嗨frnds



我在mysql中有2个表我想从table1中只选择2列并想加入table2我尝试过内连接，左连接除了它不工作之外的所有PLZ帮助



>选择年份，批次从tb1左边加入tb2到tb1;

解决方案

你的在上是完全错误的。 />


您需要一张桌子上的键和外键另一个引用第一个的列。



然后选择变为类似

 选择年，从 tb1 
  left   join  tb2  on  tb1。 key  = tb2.foreignkey 

有一个关于如何编写MySQL查询的教程at tutorialspoint [ ^ ]





如果你有很多公司要在表之间匹配的列，然后将这些列添加到ON子句。例如

在tb1.key = tb2.foreignkey 和tb1.col2 = tb2.col2和tb1.col3 = tb2.col3 等左连接tb2 

hi frnds

I have 2 tables in mysql i want to select only 2 columns from table1 and want to join on table2 i had tried inner join,left join and all but its not working plz help

> select year,batch from tb1 left join tb2 on tb1;

解决方案

Your on is completely wrong.

You will need a key on one table and a foreign key column on the other that refers back to the first one.

The select then becomes something like

select year, batch
from tb1
left join tb2 on tb1.key = tb2.foreignkey

There is a tutorial on how to write MySQL queries at tutorialspoint[^]

[Edit]
If you have many columns that you want to match on between the tables then just add those columns to the ON clause. Eg

left join tb2 on tb1.key = tb2.foreignkey and tb1.col2 = tb2.col2 and tb1.col3 = tb2.col3 etc

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