用于从2个表中获取记录的标量查询

Question

我有一个表作为tbl_employee，分别有列id，name，bco和wco。 bco和wco将int值作为其数据类型。

我有一个包含cid和country

列的表tbl_country

我想以

的形式获取记录

Name        Bco       WCO
==========================
Raj         India     USA

Answer 1

这需要加入tbl_country两次，如下所示。请注意，查询正在使用inner join，因此bco和wco都应在country表中包含匹配的记录，否则只需使用left join。

select
e.name,
c1.country as Bco,
c2.country as WCO
from tbl_employee  e
join tbl_country c1 on c1.cid = e.bco
join tbl_country c2 on c2.cid = e.wco

Answer 2

SELECT tbl_employee.id,tbl_employee.name,tbl_country.countryName 
  as BCO,tbl_country.countryName as WCO 
FROM tbl_employee 
LEFT JOIN tbl_country ON tbl_country.id = tbl_employee.bco 
RIGHT JOIN tbl_country ON tbl_country.id = tbl_employee.wco

Answer 3

试试这个：

SELECT tbl_employee.name AS name, lookup_bco.country AS Bco, lookup_wco.country AS WCO
FROM tbl_employee
INNER JOIN tbl_country AS lookup_bco ON tbl_employee.bco = lookup_bco.cid
INNER JOIN tbl_country AS lookup_wco ON tbl_employee.wco = lookup_wco.cid