如何从 SQL 内连接表中删除重复值？

Question

我有两张桌子：

表 1：

+-----------+-----------+------------------+
| ID        | Value     | other            |
+-----------+-----------+------------------+
| 123456    | 5         | 12               |
| 987654    | 7         | 15               |
| 456789    | 6         | 22               |
+-----------+-----------+------------------+

表 2：

+-----------+-----------+------------------+
| ID        | Type      | other            |
+-----------+-----------+------------------+
| 123456    | 00        | 2                |
| 123456    | 01        | 6                |
| 123456    | 02        | 4                |
| 987654    | 00        | 7                |
| 987654    | 01        | 8                |
| 456789    | 00        | 6                |
| 456789    | 01        | 16               |
+-----------+-----------+------------------+

现在我执行内部连接：

SELECT
  table1.ID, table2.TYPE, table1.value, table2.other 
FROM
  table1 INNER JOIN table2 ON table1.ID = table2.ID

这里是SQLfiddle

结果表：

+-----------+-----------+---------+------------------+
| ID        | Type      | Value   | other            |
+-----------+-----------+---------+------------------+
| 123456    | 00        | 5       | 2                |
| 123456    | 01        | 5       | 6                |
| 123456    | 02        | 5       | 4                |
| 987654    | 00        | 7       | 7                |
| 987654    | 01        | 7       | 8                |
| 456789    | 00        | 6       | 6                |
| 456789    | 01        | 6       | 16               |
+-----------+-----------+---------+------------------+

这完全是我所期望的，但不是我需要的。 因为如果我现在想获取每个 ID 的值，那么第一个原因的值会增加一倍或三倍。

所需的表：

+-----------+-----------+---------+------------------+
| ID        | Type      | Value   | other            |
+-----------+-----------+---------+------------------+
| 123456    | 00        | 5       | 2                |
| 123456    | 01        | -       | 6                |
| 123456    | 02        | -       | 4                |
| 987654    | 00        | 7       | 7                |
| 987654    | 01        | -       | 8                |
| 456789    | 00        | 6       | 6                |
| 456789    | 01        | -       | 16               |
+-----------+-----------+---------+------------------+

我试图通过计算每个 id 的行数并将 Value 的总和除以该计数来实现类似的输出，但它似乎不起作用并且不是所需的输出。

另外，我尝试分组，但这似乎没有达到预期的输出。

要提一提的是，我正在使用的数据库是一个 ORACLE SQL 数据库。

Answer 1

这个怎么样：

select table1.id
     , table2.type
     , case
           when row_number() over (partition by table1.id order by table2.type) = 1
           then table1.value
       end as "VALUE"
     , table2.other
from   table1
       join table2 on table1.id = table2.id
order by 1, 2;

（这是 Oracle SQL 语法。您的 SQL Fiddle（谢谢！）设置为 MySQL，据我所知，它没有像 row_number() 这样的分析函数。）

Answer 2

一种获得结果的方法。

  select   t1.ID,
           t2.type, 
           t1.value,
           t2.other
    from table1 t1 inner join table2 t2
    ON t1.ID = t2.ID
    inner join (select ID, min(type) mv
    from table2
    group by id) m
    on t2.id = m.id
    and t2.type = m.mv
    union all
    select t1.ID,
           t2type, 
           null,
           t2.other
    from table1 t1 inner join table2 t2
    ON t1.ID = t2.ID
    and not exists (
    select 1 from (
    select ID, min(type) mv
    from table2
    group by id) m
    where t2.id = m.id
    and t2.type = m.mv
    )

    order by id,type

Answer 3

您可以使用CASE 块来显示不等于MIN 值type 的NULL

SELECT table1.ID,
       table2.TYPE,
       CASE
          WHEN table2.TYPE =
                  MIN (table2.TYPE)
                     OVER (PARTITION BY table1.id ORDER BY table2.TYPE)
          THEN
             Table1.VALUE
       END
          VALUE,
       table2.other
  FROM table1 INNER JOIN table2 ON table1.ID = table2.ID;