如何加入左连接两列

Question

我有两个表tableCode和tableName，如下所示：

tableCode
code1, code2, code3, name3
1,     1,     1,     code31name

tableName
type, typeName, code, name
c1,       code1,        1,    code11name
c2,       code2,        1,    code21name

我想选择结果如下

1,code11name,1,code21name,1,code31name

我只知道如下，你能帮助我吗？

select m1.code1, m2.name, m1.code2, m3.name, m1.code3, m1.name3 
from tableCode m1 
left join tableName m2 on m1.code1 = m2.code and m2.type ='c1'
left join tableName m3 on m1.code1 = m3.code and m3.type ='c2'

Answer 1

您还需要一次加入。我认为您对表别名感到困惑：

select c.code1, n1.name, c.code2, n2.name, c.code3, n3.name3 
from tableCode c left join
     tableName n1
     on n1.code = c.code1 and n1.category  = 'c1' left join
     tableName n2
     on n2.code = c.code2 and n2.category  = 'c2' left join
     tableName n3
     on n3.code = c.code3 and n3.category  = 'c3';