Question

我有2张表格如下

表1 ：动物（ID是主键）

ID  |Animal
----------
1   |Dog
2   |Cat
3   |Fish
4   |Bird
5   |Elephant

表2 ：Pet（这里的ID是Animal表的外键）

ID | Animal | Name
----------
1 | Dog | Annie
1 | Dog | Buckie
2 | Cat | Conner
2 | Cat | Kitten
3 | Fish| Lala

我想编写一个SQL语句，在没有违反订单的情况下，只要出现特定宠物“狗”，就会附加一行“Fish”。

预期结果应为：

ID | Animal | Name
----------
1 | Dog | Annie
3 | Fish| NULL 
1 | Dog | Buckie
3 | Fish| NULL
2 | Cat | Conner
2 | Cat | Kitten
3 | Fish| Lala

Answer 1

我对Oracle11g不太确定，但我认为它有ROW_NUMBER。

您可以在原始表格中添加行号，然后将鱼表与相应的行号联合起来。

例如

WITH Tablex AS (
    SELECT ROW_NUMBER() OVER(ORDER BY ID, Name) AS ref_id, *
    FROM your_table
    )
SELECT ID, Animal, Name
FROM (SELECT *
      FROM Tablex
      UNION ALL
      SELECT * 
      FROM 
        (SELECT ref_id, 3 AS ID, 'Fish' AS Animal, NULL AS Name
         FROM TableX
         WHERE Animal = 'Dog'
         ) x
     ) X
ORDER BY ref_id, id

如上所述，行的顺序仅取决于ORDER BY子句，并且该顺序可能实际上并未包含在表中（如果您将其INTO置于其中）。

Answer 2

with Q as (
  select ID, Animal, Name,
         row_number() over (order by id, name) rnum
    from Pet
)
select ID, Animal, Name, rnum 
  from Q

union all

select 3, 'Fish', NULL, rnum+0.5
  from Q
 where ID=1 and name in('Annie','Buckie')
 order by rnum

Answer 3

试试这个

select tn.Id 
    , case when tt.rn = 0 then tn.Animal else 'Fish' end Animal
    , case when tt.rn = 0 then tn.Name else NULL end Name
    , tn.rn+tt.rn  rn
from (
    select ID, Animal, Name,  2 * row_number() over (order by id, name) as rn
    from pet
    ) tn
join (
     select 0 rn from dual union
     select 1 from dual
) tt on tt.rn <= case Animal when 'Dog' then 1 else 0 end
order by tn.rn+tt.rn;

用于根据先前记录有条件地选择记录的SQL语句

3 个答案: