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返回字段（即设备）匹配的查询，并将每种设备的输出限制为每个设备类型2个或更少的记录。我知道这可能不是使用多个设备的最佳方式where子句但我过去曾使用过这个或者语句，但是不能用rownum。它似乎只返回最后一个where语句。提前谢谢..

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，以便将优先级最高的元素放在顺序中。

修改

要拔出设备匹配且状态为活动的行，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

行计数可以特定于每个设备类型！

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

关于多个where子句的SQL Oracle rownum？

4 个答案: