从sql中的select语句中插入多行

Question

我有一个表需要迁移到新表。

表 A 迁移到表 B

表 A

| ID   | type |

| A1   |  A   |
| A2   |  B   |
| A3   |  A   |
| A4   | both |
| A5   |  A   |

我希望表 B 看起来像这样

表 B

| ID   | FKA  |  TYPE |

| B1   |  A1  |   Aa  |
| B2   |  A2  |   Bb  |
| B3   |  A3  |   Aa  |
| B4   |  A4  |   Aa  |
| B5   |  A4  |   Bb  |
| B6   |  A5  |   Aa  |

如果你意识到如果type是both，它会从表A向表B插入两次。

**FKA 是表 A 的外键

目前我做了 3 个查询

查询 1：

insert into tableB
select sequence1.nextVal, ID, 
(case
when type = 'A' then 'Aa'
when type = 'B' then 'Bb'
when type = 'both' then 'Aa'
else NULL
end
) from tableA

查询 2

insert into tableB
select sequence1.nextVal, ID, 
(case
when type = 'both' then 'Bb'
else 'laterdelete'
end
) from tableA

查询 3

delete from tableB where type = 'laterdelete'

谢谢大家

Answer 1

我假设 rdbms 是 Oracle。您可能希望使用这些值创建一个表（例如“tablemapping”）

 FieldFrom FieldTo
 A         Aa
 B         Bb
 both      Aa
 both      Bb

所以你可以这样做：

 Insert into tableB
 select sequence1.nextval, ID, FieldTo
    FROM tableA a 
         join tablemapping m 
           on a.type=m.fieldFrom

如果您不想有一个映射表，您可以模拟一个。

 Insert into tableb
 select sequence1.nextval, ID, FieldTo
    FROM tableA a 
         join (
               select 'both'  as FieldFrom,  'Ab'  as FieldTo from dual
                Union all
               select 'both'  as FieldFrom,  'Bb'  as FieldTo from dual
                Union all
               select 'A'  as FieldFrom,  'Aa'  as FieldTo from dual
                Union all
               select 'B'  as FieldFrom,  'Bb'  as FieldTo from dual
              ) tablemapping m 
           on a.type=m.fieldFrom

Answer 2

您可以在第一个查询中使用 union 来在 tableB 中获得所需的结果。 查询如下：

insert into tableB
select sequence1.nextVal, ID, 
(case
when type = 'A' then 'Aa'
when type = 'B' then 'Bb'
when type = 'both' then 'Aa'
else NULL
end
) from tableA
UNION
select sequence1.nextVal, ID, 
(case
when type = 'A' then 'Aa'
when type = 'B' then 'Bb'
when type = 'both' then 'Bb'
else NULL
end
) from tableA

当 type 都在 tableA 中时，上面的查询将在 tableB 中插入 Aa 和 Bb。 希望这会有所帮助。