获取表列中序列值的范围

Question

我的专栏中有一个价值列表。并想查询范围。 例如。如果值为 1,2,3,4,5,9,11,12,13,14,17,18,19

我想显示 1-5,9,11-14,17-19

Answer 1

假设每个值都存储在单独的行中，您可以在此处使用一些间隙和孤岛技术：

select case when min(val) <> max(val)
    then concat(min(val), '-', max(val))
    else min(val)
end val_range
from (select val, row_number() over(order by val) rn from mytable) t
group by val - rn
order by min(val)

这个想法是通过获取值和递增排名之间的差值来构建连续值组，递增排名是使用row_number() 计算的（在 MySQL 8.0 中可用）：

Demo on DB Fiddle：

| val_range | | :-------- | | 1-5 | | 9 | | 11-14 | | 17-19 |

在早期版本中，您可以使用相关子查询或用户变量来模拟 row_number()。第二个选项如下：

select case when min(val) <> max(val)
    then concat(min(val), '-', max(val))
    else min(val)
end val_range
from (select @rn := 0) x
cross join (
    select val, @rn := @rn + 1 rn 
    from (select val from mytable order by val) t
) t
group by val - rn
order by min(val)

Answer 2

作为其他答案的补充：

select dn.val as dnval, min(up.val) as upval 
from mytable up
join mytable dn
    on dn.val <= up.val
where not exists (select 1 from mytable a where a.val = up.val + 1)
  and not exists (select 1 from mytable b where b.val = dn.val - 1)
group by dn.val
order by dn.val;

1   5
9   9
11  14
17  19

不用说，但使用像 @GNB 这样的 OLAP 函数，效率要高几个数量级。

关于如何在 MySQL

mysql-row_number

Fiddle

编辑：

如果引入另一个维度（在本例中为 p），类似于：

select dn.p, dn.val as dnval, min(up.val) as upval 
from mytable up
join mytable dn
    on dn.val <= up.val
    and dn.p = up.p
where not exists (select 1 from mytable a where a.val = up.val + 1 and a.p = up.p)
  and not exists (select 1 from mytable b where b.val = dn.val - 1 and b.p = dn.p)
group by dn.p, dn.val
order by dn.p, dn.val;

可以使用，见Fiddle2