MySQL基础篇(01):经典实用查询案例,总结整理
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一、连接查询
图解示意图
1、建表语句
部门和员工关系表:
CREATE TABLE `tb_dept` ( `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键ID',
`deptName` varchar(30) DEFAULT NULL COMMENT '部门名称',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
CREATE TABLE `tb_emp` (
`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键ID',
`empName` varchar(20) DEFAULT NULL COMMENT '员工名称',
`deptId` int(11) DEFAULT '0' COMMENT '部门ID',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;
2、七种连接查询
- 图1:左外连接
select t1.*,t2.empName,t2.deptId from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptId;
- 图2:右外连接
select t1.*,t2.empName,t2.deptId from tb_dept t1 RIGHT JOIN tb_emp t2 on t1.id=t2.deptId;
- 图3:内连接
select t1.*,t2.empName,t2.deptId from tb_dept t1 inner join tb_emp t2 on t1.id=t2.deptId;
- 图4:左连接
查询tb_dept表特有的地方。
select t1.*,t2.empName,t2.deptId from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptId
WHERE t2.deptId IS NULL;
- 图5:右连接
查询tb_emp表特有的地方。
select t1.*,t2.empName,t2.deptId from tb_dept t1 RIGHT JOIN tb_emp t2 on t1.id=t2.deptId
WHERE t1.id IS NULL;
- 图6:全连接
select t1.*,t2.empName,t2.deptId from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptId
UNION
select t1.*,t2.empName,t2.deptId
from tb_dept t1 RIGHT JOIN tb_emp t2 on t1.id=t2.deptId
- 图7:全不连接
查询两张表互不关联到的数据。
select t1.*,t2.empName,t2.deptId from tb_dept t1 RIGHT JOIN tb_emp t2 on t1.id=t2.deptId
WHERE t1.id IS NULL
UNION
select t1.*,t2.empName,t2.deptId
from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptId
WHERE t2.deptId IS NULL
二、时间日期查询
1、建表语句
CREATE TABLE `ms_consume` ( `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键ID',
`user_id` int(11) NOT NULL COMMENT '用户ID',
`user_name` varchar(20) NOT NULL COMMENT '用户名',
`consume_money` decimal(20,2) DEFAULT '0.00' COMMENT '消费金额',
`create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 COMMENT='消费表';
2、日期统计案例
- 日期范围内首条数据
场景:产品日常运营活动中,经常见到这样规则:活动时间内,首笔消费满多少,优惠多少。
SELECT * FROM (
SELECT * FROM ms_consume
WHERE
create_time
BETWEEN '2019-12-10 00:00:00' AND '2019-12-18 23:59:59'
ORDER BY create_time
) t1
GROUP BY t1.user_id ;
- 日期之间时差
场景:常用的倒计时场景
SELECT t1.*, timestampdiff(SECOND,NOW(),t1.create_time) second_diff
FROM ms_consume t1 WHERE t1.id='9' ;
- 查询今日数据
-- 方式一SELECT * FROM ms_consume
WHERE DATE_FORMAT(NOW(),'%Y-%m-%d')=DATE_FORMAT(create_time,'%Y-%m-%d');
-- 方式二
SELECT * FROM ms_consume
WHERE TO_DAYS(now())=TO_DAYS(create_time) ;
- 时间范围统计
场景:统计近七日内,消费次数大于两次的用户。
SELECT user_id,user_name,COUNT(user_id) userIdSum FROM ms_consume WHERE create_time>date_sub(NOW(), interval '7' DAY)
GROUP BY user_id HAVING userIdSum>1;
- 日期范围内平均值
场景:指定日期范围内的平均消费,并排序。
SELECT * FROM (
SELECT user_id,user_name,
AVG(consume_money) avg_money
FROM ms_consume t
WHERE t.create_time BETWEEN '2019-12-10 00:00:00'
AND '2019-12-18 23:59:59'
GROUP BY user_id
) t1
ORDER BY t1.avg_money DESC;
三、树形表查询
1、建表语句
CREATE TABLE ms_city_sort ( `id` INT (11) NOT NULL AUTO_INCREMENT COMMENT '主键ID',
`city_name` VARCHAR (50) NOT NULL DEFAULT '' COMMENT '城市名称',
`city_code` VARCHAR (50) NOT NULL DEFAULT '' COMMENT '城市编码',
`parent_id` INT (11) NOT NULL DEFAULT '0' COMMENT '父级ID',
`state` INT (11) NOT NULL DEFAULT '1' COMMENT '状态:1启用,2停用',
`create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
`update_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '修改时间',
PRIMARY KEY (id)
) ENGINE = INNODB DEFAULT CHARSET = utf8 COMMENT = '城市分类管理';
2、直接SQL查询
SELECT t1.*, t2.parentNameFROM ms_city_sort t1
LEFT JOIN (
SELECT
m1.id,m2.city_name parentName
FROM
ms_city_sort m1,ms_city_sort m2
WHERE m1.parent_id = m2.id
AND m1.parent_id > 0
) t2 ON t1.id = t2.id;
3、函数查询
- 查询父级名称
DROP FUNCTION IF EXISTS get_city_parent_name;CREATE FUNCTION `get_city_parent_name`(pid INT)
RETURNS varchar(50) CHARSET utf8
begin
declare parentName VARCHAR(50) DEFAULT NULL;
SELECT city_name FROM ms_city_sort WHERE id=pid into parentName;
return parentName;
end
SELECT t1.*,get_city_parent_name(t1.parent_id) parentName FROM ms_city_sort t1 ;
- 查询根节点子级
DROP FUNCTION IF EXISTS get_root_child;CREATE FUNCTION `get_root_child`(rootId INT)
RETURNS VARCHAR(1000) CHARSET utf8
BEGIN
DECLARE resultIds VARCHAR(500);
DECLARE nodeId VARCHAR(500);
SET resultIds = '%';
SET nodeId = cast(rootId as CHAR);
WHILE nodeId IS NOT NULL DO
SET resultIds = concat(resultIds,',',nodeId);
SELECT group_concat(id) INTO nodeId
FROM ms_city_sort WHERE FIND_IN_SET(parent_id,nodeId)>0;
END WHILE;
RETURN resultIds;
END ;
SELECT * FROM ms_city_sort WHERE FIND_IN_SET(id,get_root_child(5)) ORDER BY id ;
四、源代码地址
GitHub·地址https://github.com/cicadasmile/mysql-data-base
GitEE·地址
https://gitee.com/cicadasmile/mysql-data-base
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