选择行中具有相同值的行

Question

我有2张这样的表：

表1

    ID - 4PP - woonplaats
    1 - 9044 - Beetgum
    2 - 9045 - Beetgummermole    
    3 - 1028 - Amsterdam
    4 - 1029 - Amsterdam
    5 - 1030 - Amsterdam 

表2

    ID - 4PP - Regio
    1 - 9044 - 2
    2 - 9045 - 2
    3 - 1028 - 4
    4 - 1029 - 4
    5 - 1030 - 4

我想从表2中选择所有4PP，其中表1中的“woonplaats”是Beetgum，表格可以通过4PP加入。所以查询的结果必须是：9044,9045

Answer 1

怎么样：

select t2b.Regio from table1 t1 
 join table2 t2a on t1.4pp = t2a.4pp
 join table2 t2b on t2a.Regio = t2b.Regio
 where t1.woonplaats = "Beetgum";

Answer 2

select 4PP
from table1 inner join table2 using (4PP)
where table1.woonplaats like '%Beetgum%'