sql - 多个where子句上的SQL Oracle rownum？

Question

select * from MYTABLE t 
where EQUIPMENT = 'KEYBOARD' and ROWNUM <= 2 or
EQUIPMENT = 'MOUSE' and ROWNUM <= 2 or
EQUIPMENT = 'MONITOR' and ROWNUM <= 2; 

我正在尝试运行一个查询，该查询返回字段（即设备）上的匹配项，并将每种设备类型的输出限制为每种设备类型 2 条或更少的记录。我知道这可能不是使用多个 where 子句的最佳方法，但是我过去曾使用过它，由 or 语句分隔，但不适用于 rownum。似乎它只返回最后一个 where 语句。提前致谢..

Answer 1

WITH numbered_equipment AS (
  SELECT t.*,
         ROW_NUMBER() OVER( PARTITION BY EQUIPMENT ORDER BY NULL ) AS row_num
  FROM   MYTABLE t 
  WHERE  EQUIPMENT IN ( 'KEYBOARD', 'MOUSE', 'MONITOR' )
)
SELECT *
FROM   numbered_equipment
WHERE  row_num <= 2;

SQLFIDDLE

如果要根据其他列优先选择哪些行，则修改ORDER BY NULL查询部分以将最高优先级元素放在顺序中的首位。

编辑

要仅拉出设备匹配且状态处于活动状态的行，请使用：

WITH numbered_equipment AS (
  SELECT t.*,
         ROW_NUMBER() OVER( PARTITION BY EQUIPMENT ORDER BY NULL ) AS row_num
  FROM   MYTABLE t 
  WHERE  EQUIPMENT IN ( 'KEYBOARD', 'MOUSE', 'MONITOR' )
  AND    STATUS = 'Active'
)
SELECT *
FROM   numbered_equipment
WHERE  row_num <= 2;

SQLFIDDLE

Answer 2

行数可以特定于每种设备类型！

SELECT * FROM MYTABLE t 
where EQUIPMENT = 'KEYBOARD' and ROWNUM <= 2 
UNION ALL
SELECT * FROM MYTABLE t
WHERE EQUIPMENT = 'MOUSE' and ROWNUM <= 2
UNION ALL
SELECT * FROM MYTABLE t
WHERE EQUIPMENT = 'MONITOR' and ROWNUM <= 2; 

Answer 3

试试这个：

select * from (
    select * from MYTABLE t  where EQUIPMENT = 'KEYBOARD' and ROWNUM <= 2 
    union
    select * from MYTABLE t  where EQUIPMENT = 'MOUSE' and ROWNUM <= 2 
    union
    select * from MYTABLE t  where EQUIPMENT = 'MONITOR' and ROWNUM <= 2 )

Answer 4

尝试：

select * from MYTABLE t  where EQUIPMENT = 'KEYBOARD' and ROWNUM <= 2 
union
select * from MYTABLE t  where EQUIPMENT = 'MOUSE' and ROWNUM <= 2 
union
select * from MYTABLE t  where EQUIPMENT = 'MONITOR' and ROWNUM <= 2