mysql的CUDR

Posted 2020-12-08 dai_213

数据库的CUDR

一、create

create table tbl_name(

attribute1 int,

attribute2 varchar20,

)

二、update

update

三、delect

 

四、read

数据的读操作是重点

4.1 简单的数据记录查询

1、读取不重复数据 distinct关键字 select distinct va1 val2,,,valn from tbl_xxx # 这里面是值的val,val2...valn的并集不同就显示 select distinct house_title from tbl_house; 2、查询过程中实现四则运算 select ename sla*12 from tbl_xxx; select ename, sla*12 as yearsalary from tbl_xxx; 3、设置显示数据的格式 select contact(ename,‘雇员年薪为:‘,sla*12) yearsalary from tbl_xxx;

 

 

 

 

 

 

 

 

 

 

 

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1、读取不重复数据 distinct关键字

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select distinct va1 val2,,,valn from tbl_xxx    # 这里面是值的val,val2...valn的并集不同就显示

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select distinct house_title from tbl_house;

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2、查询过程中实现四则运算

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select ename sla*12 from tbl_xxx;

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select ename, sla*12 as yearsalary from tbl_xxx;

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3、设置显示数据的格式

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select contact(ename,‘雇员年薪为:‘,sla*12) yearsalary from tbl_xxx;

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4.2 条件数据记录查询

select field1,field2 from tbl_xxx where condition 这里面的condition，可以有很多类型 1、带关系运算符和逻辑运算符的条件查询 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10; 2、带 between and 关键字的条件查询 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10 and field2 between 10 and 100; 3、带 is null 关键字的条件查询 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10 and field3 is null; 4、带 in 的关键字的条件查询 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10 and field4 in (12,12,3,4,5); 5、带 like 关键字的条件查询 select distinct title,location from house_price_list2 where location like ‘%麓山%‘;

 

 

 

 

 

 

 

 

 

 

 

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select field1,field2 from tbl_xxx where condition

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这里面的condition，可以有很多类型

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1、带关系运算符和逻辑运算符的条件查询

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10;

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2、带 between and 关键字的条件查询

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10 and field2 between 10 and 100;

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3、带 is null 关键字的条件查询

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10 and field3 is null; 

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4、带 in 的关键字的条件查询 

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ and field1>10 and field4 in (12,12,3,4,5);

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5、带 like 关键字的条件查询  

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘;

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4.3 排序数据记录查询

1、 单字段排序 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location; select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location desc; 降序 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location asc; 升序 2、 多字段排序 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location desc,title desc;

 

 

 

 

 

 

 

 

 

 

 

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1、 单字段排序

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location;

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location desc; 降序

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select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location asc; 升序

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2、 多字段排序

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 select distinct title,location from house_price_list2 where location like ‘%麓山%‘ order by location desc,title desc;

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4.4 限制数据记录查询数量

select * from house_price_list2 limit 100; select * from house_price_list2 limit 0,100; # 初始位置0，到100行

 

 

 

 

 

 

 

 

 

 

 

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select * from house_price_list2 limit 100;

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select * from house_price_list2 limit 0,100;   # 初始位置0，到100行

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4.5 统计函数和分组数据记录查询

1、函数类型： count() avg() sum() max() min() select count(*) from house_price_list2 where location like ‘%马%‘; 这里的*指的所有字段 一般形式如 select function(field1) from tbl_xxx where condition 2、简单分组查询 select * from house_price_list2 group by house_info; # 简单分组查询，对house_info分组，然后显示每个分组的一条记录 仅仅使用简单分组查询是没有什么实际意义，因为这个显示的一条数据是随机的 3、实现统计功能分组查询 select GROUP_CONCAT(house_price) FROM house_price_list2 GROUP BY house_info; 一般形式如下 select group_concat(field) from tbl_xxx where condition group by field; 这种分组查询，可以看到每个组中的字段值

 

 

 

 

 

 

 

 

 

 

 

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1、函数类型： count() avg() sum() max() min()

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select count(*) from house_price_list2 where location like ‘%马%‘; 

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这里的*指的所有字段

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一般形式如

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select function(field1) from tbl_xxx where condition

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2、简单分组查询

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select * from house_price_list2 group by house_info;   # 简单分组查询，对house_info分组，然后显示每个分组的一条记录

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仅仅使用简单分组查询是没有什么实际意义，因为这个显示的一条数据是随机的

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3、实现统计功能分组查询

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select GROUP_CONCAT(house_price) FROM house_price_list2 GROUP BY house_info;

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一般形式如下

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select group_concat(field) from tbl_xxx where condition group by field;

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这种分组查询，可以看到每个组中的字段值

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