Question

我有一个表foo及其主键id和其他一些列。我的目标是找到包含id=3和id=4的行以及包含id=6和id=7的行，以及id=5行 - 以防我想查找2个最接近的上一行和下一行。

如果只有一行或没有这样的行（例如id=2只有前一行），我想只获得可能的行。

问题是可能缺少某些行。

是否有通常的做法来进行此类查询？

Answer 1

我会尝试以下方法：

SELECT * FROM table WHERE id > ? ORDER BY id ASC LIMIT 2

接着是

SELECT * FROM table WHERE id <= ? ORDER BY id DESC LIMIT 2

您可以将以上内容合并到以下内容中：

SELECT * FROM table WHERE id > ? ORDER BY id ASC LIMIT 2
UNION
SELECT * FROM table WHERE id <= ? ORDER BY id DESC LIMIT 2

Answer 2

这是一种可能的解决方案，它通过对所有记录进行编号并获取行号大于或小于所选ID的行数。

create table foo(id int);
insert into foo values (1),(2),(4),(6),(7),(8),(11),(12);

-- using ID = 6

with rnum as
(
    select id, row_number() over (order by id) rn
    from foo
)
select *
from   rnum
where  rn >= (select rn from rnum where id = 6) - 2
and    rn <= (select rn from rnum where id = 6) + 2;

id | rn
-: | -:
 2 |  2
 4 |  3
 6 |  4
 7 |  5
 8 |  6

-- using ID = 2

with rnum as
(
    select id, row_number() over (order by id) rn
    from foo
)
select *
from   rnum
where  rn >= (select rn from rnum where id = 2) - 2
and    rn <= (select rn from rnum where id = 2) + 2;

id | rn
-: | -:
 1 |  1
 2 |  2
 4 |  3
 6 |  4

dbfiddle here

Answer 3

我认为这符合您的描述。

Select * from table where id between @n-2 and @n+2 and id <> @n

Answer 4

一种方法是：

with your_table(id) as(
    select 1 union all
    select 2 union all
    select 4 union all
    select 5 union all
    select 10 union all
    select 11 union all
    select 12 union all
    select 13 union all
    select 14  
)

select * from (
    (select * from your_table where id <= 10 order by id desc limit 3+1)
    union all
    (select * from your_table where id > 10 order by id limit 3)
) t
order by id

（此处10是起点，3是您想要的n行

如何为表中的特定行获取最接近的n行？

4 个答案: