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.deptIdWHERE 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.deptIdWHERE 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.deptIdUNIONselect 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.deptIdWHERE t1.id IS NULLUNIONselect t1.*,t2.empName,t2.deptId from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptIdWHERE 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_consumeWHEREcreate_time BETWEEN '2019-12-10 00:00:00' AND '2019-12-18 23:59:59'ORDER BY create_time) t1GROUP 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_moneyFROM ms_consume tWHERE t.create_time BETWEEN '2019-12-10 00:00:00' AND '2019-12-18 23:59:59'GROUP BY user_id) t1ORDER 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 t1LEFT JOIN (SELECTm1.id,m2.city_name parentNameFROMms_city_sort m1,ms_city_sort m2WHERE m1.parent_id = m2.idAND 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 utf8begin     declare parentName VARCHAR(50) DEFAULT NULL;    SELECT city_name FROM ms_city_sort WHERE id=pid into parentName;    return parentName;endSELECT 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 ;

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