当前位置:网站首页>嵌入式数据库开发编程(五)——DQL
嵌入式数据库开发编程(五)——DQL
2022-07-05 04:56:00 【光追雨】
一、数据集
二、查询记录
select field1,field2,…fieldn… from 表名 [where 条件]
select*from 表名 [where 条件]
三、查询不重复的记录
- select distinct 字段 from 表名
- select distinct name from students;//4查询名字不相同的学生;
- select distinct name,age from students;//查询名字和年龄同时不同的学生
- distinct必须放在最开头
- distinct只能使用需要去重的字段进行操作
- distinct去重多个字段时,含义是:几个字段同时重复时才会被过滤。
四、条件查询
select字段from表名where条件; select*from student where sex='男’and age>20; //查询性别是男,并且年龄大于20
where后面的条件可以用>、<、>=、<=、!=等多种比较运算符,多个条件之间可以用or、and等逻辑运算符
五、排序和限制
5.1 排序
5.2 限制
六、聚合
6.1 聚合函数
七、多表查询
八、表连接
边栏推荐
- Listview is added and deleted at the index
- Sixth note
- 2021 electrician Cup - high speed rail traction power supply system operation data analysis and equivalent modeling ideas + code
- AutoCAD - full screen display
- 【acwing】836. Merge sets
- 中国AS树脂市场调研与投资预测报告(2022版)
- AutoCAD - command repetition, undo and redo
- Animation
- mysql审计日志归档
- Panel panel of UI
猜你喜欢
Pdf to DWG in CAD
2021-10-29
【acwing】836. Merge sets
LeetCode之单词搜索(回溯法求解)
数论函数及其求和 待更新
Emlog博客主题模板源码简约好看响应式
2021 higher education social cup mathematical modeling national tournament ABCD questions - problem solving ideas - Mathematical Modeling
2022 thinking of Mathematical Modeling B problem of American college students / analysis of 2022 American competition B problem
Thinking of 2022 American College Students' mathematical modeling competition
3dsmax snaps to frozen objects
随机推荐
How much do you know about 3DMAX rendering skills and HDRI light sources? Dry goods sharing
Lua wechat avatar URL
Sixth note
#775 Div.1 C. Tyler and Strings 组合数学
Recherche de mots pour leetcode (solution rétrospective)
Unity enables mobile phone vibration
cocos_ Lua listview loads too much data
Pause and resume of cocos2dx Lua scenario
数论函数及其求和 待更新
Emlog blog theme template source code simple good-looking responsive
Forecast report on research and investment prospects of Chinese wormwood industry (2022 Edition)
2021 higher education social cup mathematical modeling national tournament ABCD questions - problem solving ideas - Mathematical Modeling
Séparation et combinaison de la construction du système qualité
JMeter -- distributed pressure measurement
2022 thinking of Mathematical Modeling B problem of American college students / analysis of 2022 American competition B problem
775 Div.1 B. integral array mathematics
Understand encodefloatrgba and decodefloatrgba
xss注入
【acwing】837. Number of connected block points
[groovy] closure (closure call is associated with call method | call () method is defined in interface | call () method is defined in class | code example)