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mysql的基础命令
2022-07-06 06:26:00 【luckyyuanyuan】
sql区别大小写问题
创建数据表:
CREATE TABLE IF NOT EXISTS `runoob_tbl`(
`runoob_id` INT UNSIGNED AUTO_INCREMENT,
`runoob_title` VARCHAR(100) NOT NULL,
`runoob_author` VARCHAR(40) NOT NULL,
`submission_date` DATE,
PRIMARY KEY ( `runoob_id` )
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
1. 设置字段的属性为 NOT NULL, 在操作数据库时如果输入该字段的数据为NULL ,就会报错。
2. AUTO_INCREMENT定义列为自增的属性,一般用于主键,数值会自动加1。
3. PRIMARY KEY关键字用于定义列为主键。 您可以使用多列来定义主键,列间以逗号分隔。
4. ENGINE 设置存储引擎,CHARSET 设置编码。
根据表中某一列的“PH”字段查找数据,并限制只显示查找的前1000行
select * from dm_oss.d_f_oss_device_service_info where device_id like '%PH%' limit 1000
查询数据某一列中有哪些值(去重)
select distinct device_id from dm_oss.d_f_oss_device_service_info where device_id
指定被插入列名和值进行插入:
INSERT INTO table_name (column1,column2,column3,...)
VALUES (value1,value2,value3,...);
在 “device_id ” 字段中查询属性值中含有 “PH” 的数据,并限制只展现1000行
select * from device_service_info where device_id like '%PH%' limit 1000
select * from device_basic_info where device_id like '%PH%' limit 1000
案例一: 多表联合查询与统计
表1:device_service_info
表2:device_basic_info
步骤1:查询1.4.9类的版本
// 在 “software_version ” 字段中查询属性值中含有 “1.4.9” 的数据
select device_id, description, software_version from device_basic_info having software_version like '%1.4.9%'
步骤2:根据service_start_time 字段选择某一段时间的数据
select device_id, service_id from device_service_info having service_start_time between "${day_start}" and "${day_end}"
步骤3:计算每个设备在指定的某段时间内的服务次数
select device_id, count(service_id) as service_sum from (select device_id, service_id from device_service_info having service_start_time between "${day_start}" and "${day_end}") group by device_id
步骤4:拼接两张表的信息,采取内连接,取其交集;
select t1.device_id, t1.service_sum, t2.description, software_version from ((select device_id, count(service_id) as service_sum from (select device_id, service_id from dm_oss .d_f_oss_device_service_info having service_start_time between "${day_start}" and "${day_end}") group by device_id) t1) inner join ((select device_id, description, software_version from dm_oss.d_f_oss_device_basic_info having software_version like '%1.4.9%') t2 )on t1.device_id = t2.device_id
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