22 lines
1.1 KiB
SQL
22 lines
1.1 KiB
SQL
-- 窗口函数
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-- row_number(): 对相等的值【不区分】，相当于行号，相等的值对应的排名不同，序号从1到n连续
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-- rank(): 相等的值排名相同，但若有相等的值，则序号从1到n不连续。符合一般人思维中的排名
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-- dense_rank(): 对相等的值排名相同，但序号从1到n连续
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-- 先按num分区，每个区内按id排序
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select id, num, id - row_number() over (partition by num order by id) as rnk
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from employee;
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-- 找出所有至少连续出现三次的数字
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-- 先按num分区，每个区内按id排序
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-- 一个分区内，如果数字连续，那么id会不断+1，row_number()也会不断+1，id - row_number()差值不变
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-- 在按照id - row_number()聚合，使用count(*)统计，count(*)的结果就是连续出现的次数
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select r.num, r.rnk, count(*)
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from (select num, id - row_number() over (partition by num order by id) as rnk from employee) as r
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group by r.num, r.rnk;
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select distinct r.num as ConsecutiveNums
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from (select num, id - row_number() over (partition by num order by id) as rnk from employee) as r
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group by r.num, r.rnk
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having count(*) >= 3
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limit 1; |