From 83092fc2df23a40770c662bba5911cc47930c41f Mon Sep 17 00:00:00 2001
From: JIAL <2287346125@qq.com>
Date: Sat, 18 Nov 2023 11:09:14 +0800
Subject: [PATCH] Initial commit

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 VSCode/SQL笔记.sql | 107 +++++++++++++++++++++++++++++++++++++++++++++
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 create mode 100644 VSCode/SQL笔记.sql

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diff --git a/VSCode/SQL笔记.sql b/VSCode/SQL笔记.sql
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+mysql自动排序函数dense_rank() over()、rank() over()、row_num() over()用法和区别
+区别：
+rank()：是并列排序，会跳过重复序号
+dense_rank()：是并列排序，不会跳过重复序号
+row_number()：是顺序排序，不跳过任何一个序号，就是行号
+
+
+create table students(
+	id int(11)  auto_increment primary key,
+	name varchar(50) not null, 
+	score int(4) not null
+	);
+ 
+insert into students(name,score) values
+('zhangsan', 100),
+('lisi', 99),
+('wangwu', 100), 
+('trx', 90), 
+('pjf', 99), 
+('wzm', 96);
+
+
+mysql> select * from students;
++----+----------+-------+
+| id | name     | score |
++----+----------+-------+
+|  1 | zhangsan |   100 |
+|  2 | lisi     |    99 |
+|  3 | wangwu   |   100 |
+|  4 | trx      |    90 |
+|  5 | pjf      |    99 |
+|  6 | wzm      |    96 |
++----+----------+-------+
+
+使用三种不同的方法进行排序：
+select 
+    id, 
+    name, 
+    rank() over(order by score desc) `rank`,
+    row_number() over(order by score desc) `row_number`,
+    dense_rank() over(order by score desc) `dense_rank`
+from students;
+ 
+--------------------------------- 结果 ------------------------------------
++----+----------+-------+------+------------+------------+
+| id | name     | score | rank | row_number | dense_rank |
++----+----------+-------+------+------------+------------+
+|  1 | zhangsan |   100 |    1 |          1 |          1 |
+|  3 | wangwu   |   100 |    1 |          2 |          1 |
+|  2 | lisi     |    99 |    3 |          3 |          2 |
+|  5 | pjf      |    99 |    3 |          4 |          2 |
+|  6 | wzm      |    96 |    5 |          5 |          3 |
+|  4 | trx      |    90 |    6 |          6 |          4 |
++----+----------+-------+------+------------+------------+
+
+
+Sql窗口分析函数【lead、lag详解】
+表：Logs
+
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| id          | int     |
+| num         | varchar |
++-------------+---------+
+在 SQL 中，id 是该表的主键。
+id 是一个自增列。
+找出所有至少连续出现三次的数字。
+
+返回的结果表中的数据可以按 任意顺序 排列。
+
+结果格式如下面的例子所示：
+示例 1:
+输入：
+Logs 表：
++----+-----+
+| id | num |
++----+-----+
+| 1  | 1   |
+| 2  | 1   |
+| 3  | 1   |
+| 4  | 2   |
+| 5  | 1   |
+| 6  | 2   |
+| 7  | 2   |
++----+-----+
+输出：
+Result 表：
++-----------------+
+| ConsecutiveNums |
++-----------------+
+| 1               |
++-----------------+
+答案：
+select
+distinct p.num as ConsecutiveNums
+from(
+    select
+    id,
+    num,
+    lag(num,1)over(order by id) num1,
+    lag(num,2)over(order by id) num2
+    from
+    Logs
+) p
+where
+p.num = p.num1 and p.num1  = p.num2
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