sql - 如何计算表中连续的重复项？

Question

我有以下问题:
想找到连续的重复项

SLNO   NAME     PG   
1       A1      NO                   
2       A2      YES              
3       A3      NO           
4       A4      YES          
6       A5      YES          
7       A6      YES          
8       A7      YES      
9       A8      YES  
10      A9      YES
11      A10     NO 
12      A11     YES 
13      A12     NO 
14      A14     NO

我们将考虑 PG 列的值，我需要输出为 6，这是最大连续重复的计数。

Answer 1

可以用 Tabibitosan 方法完成。运行这个，理解它:

with a as(
select 1 slno, 'A' pg from dual union all
select 2 slno, 'A' pg from dual union all
select 3 slno, 'B' pg from dual union all
select 4 slno, 'A' pg from dual union all
select 5 slno, 'A' pg from dual union all
select 6 slno, 'A' pg from dual 
)
select slno, pg, newgrp, sum(newgrp) over (order by slno) grp
from( 
    select slno, 
           pg, 
           case when pg <> nvl(lag(pg) over (order by slno),1) then 1 else 0 end newgrp
    from a
    );

Newgrp 表示找到了一个新组。

结果:

SLNO PG NEWGRP GRP
1    A  1      1
2    A  0      1
3    B  1      2
4    A  1      3
5    A  0      3
6    A  0      3

现在，只需使用带有计数的组，即可找到出现次数最多的组:

with a as(
select 1 slno, 'A' pg from dual union all
select 2 slno, 'A' pg from dual union all
select 3 slno, 'B' pg from dual union all
select 4 slno, 'A' pg from dual union all
select 5 slno, 'A' pg from dual union all
select 6 slno, 'A' pg from dual 
),
b as(
select slno, pg, newgrp, sum(newgrp) over (order by slno) grp
from( 
    select slno, pg, case when pg <> nvl(lag(pg) over (order by slno),1) then 1 else 0 end newgrp
    from a
    )
)
select max(cnt)
from (
    select grp, count(*) cnt
    from b
    group by grp
    );