从表JOIN中获取两个字段的值 [英] Get the values of two fields from a table JOIN

问题描述

我有一个名为districts的mysql表，其中存储了所有区及其ID.我还有另一个名为tbl_units的表，其中保存了office_address，office_district，factory_address，factory_district之类的单元详细信息.

I have a mysql table called districts where all the districts and their id's are stored. I have another table called tbl_units where unit details such as office_address, office_district, factory_address, factory_district are saved.

现在，如果要通过加入两个表来从其ID中获取区域的名称，我该如何编写查询?因为

Now if want to get the names of the districts from their id's by JOIN ing the two tables, how should I write the query ? Because

SELECT u.*, d.district_name
FROM  tbl_unit_details as u,
    tbl_districts as d 
WHERE u.unit_id = '$unit_id' 
    AND u.district_id = d.district_id 
    AND u.factory_district_id = d.district_id 
ORDER BY unit_name

仅返回办公室的第一个名称，即地区名称.

returns only the first , i.e. district name of office.

推荐答案

两次将districts表加入units表；每个地区类型一次.使用别名来区分分区表的每个实例.如果愿意，可以包含可选的AS关键字.

Join the districts table to the units table twice; once for each district type. Use aliases to distinguish each instance of the district table. If you like, you can include the optional AS keyword.

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