From 7b1465fc4ec429b40f75b7cb67d5c13a3ac9f696 Mon Sep 17 00:00:00 2001
From: Fortern <blueten.ki@gmail.com>
Date: Tue, 4 Nov 2025 21:43:10 +0800
Subject: [PATCH] =?UTF-8?q?PostgreSQL=20=E7=AA=97=E5=8F=A3=E5=87=BD?=
 =?UTF-8?q?=E6=95=B0?=
MIME-Version: 1.0
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---
 PostgreSQL/windows_fun.sql | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 PostgreSQL/windows_fun.sql

diff --git a/PostgreSQL/windows_fun.sql b/PostgreSQL/windows_fun.sql
new file mode 100644
index 0000000..0a4a96f
--- /dev/null
+++ b/PostgreSQL/windows_fun.sql
@@ -0,0 +1,22 @@
+-- 窗口函数
+-- 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
+-- 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
+-- dense_rank(): 对相等的值排名相同，但序号从1到n连续
+
+-- 先按num分区，每个区内按id排序
+select id, num, id - row_number() over (partition by num order by id) as rnk
+from employee;
+
+-- 找出所有至少连续出现三次的数字
+-- 先按num分区，每个区内按id排序
+-- 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
+-- 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
+select r.num, r.rnk, count(*)
+from (select num, id - row_number() over (partition by num order by id) as rnk from employee) as r
+group by r.num, r.rnk;
+
+select distinct r.num as ConsecutiveNums
+from (select num, id - row_number() over (partition by num order by id) as rnk from employee) as r
+group by r.num, r.rnk
+having count(*) >= 3
+limit 1;
\ No newline at end of file