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# ThingsCloud | ||
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参考,参考,绝对可以参考。 | ||
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[官方网站](https://www.thingscloud.xyz/) |
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# 概述 | ||
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物联网行业的一些业务分析、公司分析、行业分析。 |
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# MySQL 笔记 | ||
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### WITH 查询 | ||
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MySQL 语句 WITH 是 MySQL 8.0 中的一个新特性,用于帮助简化复杂查询以及提高查询效率。在大多数情况下,查询都需要多次嵌套使用,这导致查询语句写得很长且难以维护。WITH 语句就是用来解决这个问题的,它是一种临时表的方式,得到的结果集可以作为查询的结果集。在 WITH 语句中,可以定义多个别名,然后嵌套使用。 | ||
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```sql | ||
WITH t1 AS ( | ||
SELECT col1 FROM table1 | ||
), | ||
t2 as ( | ||
SELECT col1 FROM table2 | ||
) | ||
--使用 | ||
SELECT * FROM t1 INNER JOIN t2 ON t1.col1 = t2.col1; | ||
``` | ||
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在这个例子中,我们定义了两张表,t1 和 t2,然后使用了这两张表来进行查询,这样我们就可以避免在查询语句中多次嵌套使用相同的子查询,并且也不需要为每个查询定义一个临时表。 | ||
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with 特性: | ||
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- with 其实就是一个子查询抽取出来,换了一个别名 | ||
- 和视图的区别:with as 等同于一次性视图,只会持续到下一个查询。在之后就不能再被引用 | ||
- 主要用于简化复杂的 数据集 和 递归 | ||
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其实 WITH 表达式除了和 SELECT 一起用, 还可以有下面的组合: | ||
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insert with 、with update、with delete、with with、with recursive(可以模拟数字、日期等序列)、WITH 可以定义多张表 | ||
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```sql | ||
with_clause: | ||
WITH [RECURSIVE] | ||
cte_name [(col_name [, col_name] ...)] AS (subquery) | ||
[, cte_name [(col_name [, col_name] ...)] AS (subquery)] ... | ||
``` | ||
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### 递归共用表达式 with recursive | ||
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```sql | ||
WITH RECURSIVE cte (n) AS | ||
( | ||
SELECT 1 | ||
UNION ALL | ||
SELECT n + 1 FROM cte WHERE n < 5 | ||
) | ||
SELECT * FROM cte; | ||
``` | ||
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### 参考文档 | ||
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- [MySQL 8.0 with 语法(cte)](https://halo.sherlocky.com/archives/mysql-8-cte) | ||
- [MySQL 8.0 官方文档](https://dev.mysql.com/doc/refman/8.0/en/preface.html) |
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# 概述 | ||
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存储数据的服务统一成为数据库,包括但不限于: | ||
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- 关系数据库 msyql、oracle 等 | ||
- 非关系数据库 redis、MongoDB 等 |
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# 概述 | ||
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一种虚拟技术。 |
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# 概述 | ||
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所有用户看到的界面,统一成为前端,包括但不限于: | ||
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- PC WEB | ||
- 移动端 WEB | ||
- 小程序 | ||
- 桌面程序 |
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# 概述 | ||
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写代码用到的一套规范及其延伸工具。 |
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# 概述 | ||
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跨越编程语言的一些套路。 |
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# 概述 | ||
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主要使用 Java,中间件可集成或独立部署。 | ||
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- MQTT Broker 采用 hivemq 集成 | ||
- redis | ||
- mysql | ||
- kafka | ||
- influxdb |
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# 概述 | ||
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一般需要包括如下内容: | ||
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- Jenkins 持续集成、部署 | ||
- Grafana+哨兵 监控服务 | ||
- 各种运维脚本 |