Question

假设我有下表：

Table Files
 id
 size

在伪SQL中我需要这个处理之王：

select id
where
size < S1 and (limit this clause to N1 results)
or
size > S2 and (limit this clause to N2 results)

我知道Oracle定义rownum关键字来限制结果。

但就我而言，这不起作用。

这需要子选择吗？怎么样？可以使用多个子选择吗？

（这个SQL将由一个带有其他where子句的java程序生成，这使得使用subselects很困难。）

编辑：我需要过滤的不仅仅是不同的尺寸。

解决

SELECT * 
FROM Files
WHERE
    someField = 'stuff'
AND
    someOtherField = 'other stuff'
AND
(
    SELECT id FROM Files WHERE size <= S1 AND ROWNUM <= N1
    UNION
    SELECT id FROM Files WHERE size > S2 AND ROWNUM <= N2
)

Answer 1

使用UNION：

SELECT *
FROM (
    SELECT 'low' AS "which", "id"
    FROM Files
    WHERE "size" < S1)
WHERE ROWNUM <= N1

UNION

SELECT *
FROM (
    SELECT 'high' AS "which", "id"
    FROM Files
    WHERE "size" >= S1)
WHERE ROWNUM <= N2

DEMO

Answer 2

假设条款独立（它们是您的例子），您可以使用union all执行此操作：

select id
. . .
where size < S1 and rownum <= N1
union all
select id
. . .
where size > S1 and rownum <= N2

如果您不想重复from子句（因为它很复杂），您可以使用CTE：

with t as (<blah blah blah>)
select *
from ((select id from t where size < S1 and rownum <= N1) union all
      (select id from t where size > S1 and rownum <= N2)
     ) x

Answer 3

使用此查询解决

SELECT * 
FROM Files
WHERE
    someField = 'stuff'
AND
    someOtherField = 'other stuff'
AND
(
    SELECT id FROM Files WHERE size <= N1  AND ROWNUM <= N1
    UNION
    SELECT id FROM Files WHERE size  > N2  AND ROWNUM <= N2
)

SQL限制导致where子句

3 个答案: