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，该查询在字段(即设备)上返回匹配项，并将每种设备类型的输出限制为 2 条记录或更少。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

如果要根据其他列确定选择哪些行的优先级，请修改查询的 ORDER BY NULL 部分，将优先级最高的元素放在首位。

编辑

要拔出设备匹配且状态为事件的行，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