MySQL语句：将行值拆分为新列

Question

使用MySQL我需要为table1中的每个用户返回新的名/姓列。

 
**Table1** 
uid 
1 
2 

**Table2** 
id fid uid field_value 
1 1  1  Joe 
2 2  1  Blow 
3 1  2  Joe 
4 2  2  Blogs 

**Result** 
uid first_name last_name 
1  Joe   Blow 
2  Joe   Blogs 

Answer 1

解决方法很简单，

select t1.uid, t21.field_value first_name, t22.field_value last_name 
from table1 t1, table2 t21, table2 t22 
where t1.uid=t21.uid and t1.uid=t22.uid and t21.fid=1 and t22.fid=2 

Answer 2

假设你有列FIRST_NAME和姓氏在表2：

select uid, first_name, last_name from table1 left join table2 on table1.uid=table2.uid 

Answer 3

这应该这样做（未测试）：

select a.uid, a.field_value first_name, b.field_value last_name 
from table2 a inner join table2 b on a.uid = b.uid 
where a.fid = 1 and b.fid = 2