如何使用 SQL 或 HQL 连接父表和子表以获得以下内容

Question

给定如下表 1 和表 2 如何 return 结果集如下所示？

表 1

TBL1_PK     TBL1_COL2
1            A

表 2

TBL2_PK  TABLE1_FK    ROLE_CD           FIRST_NAME  LAST_NAME
1      1           ROLE_1       DEF   GHI
2      1           ROLE_2       JKL   MNP
3      1           ROLE_3       RST   UVW

结果

TBL1_COL2  ROLE_1_FIRST_NAME ROLE1_LAST_NAME ROLE_2_FIRST_NAME ROLE_2_LAST_NAME
A          DEF               GHI             JKL               MNP

Answer 1

您可以使用聚合来执行此操作：

select t1.TBL1_COL2,
    max(case 
            when t2.role_cd = 'ROLE_1'
                then t2.first_name
            end) ROLE_1_FIRST_NAME,
    max(case 
            when t2.role_cd = 'ROLE_1'
                then t2.last_name
            end) ROLE1_LAST_NAME,
    max(case 
            when t2.role_cd = 'ROLE_2'
                then t2.first_name
            end) ROLE_2_FIRST_NAME,
    max(case 
            when t2.role_cd = 'ROLE_2'
                then t2.last_name
            end) ROLE2_LAST_NAME
from table1 t1
join table2 t2 on t1.tbl1_pk = t2.table1_fk
group by t1.TBL1_COL2

Answer 2

将 table 1 加入 table 2 两次，使用 2 个不同的别名。然后根据需要限制别名以从一个获得 role_1 并从另一个获得 role_2

select
 T1.TBL1_COL2 as "TBL1_COL2",
 T2R1.FIRST_NAME as "Role_1_first_name",
 T2R1.Last_name as "Role_1_last_name",
 T2R2.First_name as "Role_2_first_name",
 T2R2.Last_name as "Role_2_last_name"
from 
   Table1 as T1
 inner join Table2 as T2R1 on T1.TBL1_PK = T2R1.Table1_fk
 inner join Table2 as T2R2 on T2.TBL1_PK = T2T2.Table1_fk
where
    T2R1.role_cd = "Role_1"
and T2T2.role_cd = "Role_2";

如何使用 SQL 或 HQL 连接父表和子表以获得以下内容

How to join parent and child tables to get the following using SQL or HQL

sql

hql