MySQL基礎篇(01)：經典實用查詢案例，總結整理

發布時間：2020-02-26 22:25:21

來源：51CTO

閱讀：244

作者：知了一笑

本文源碼：GitHub·點這里 || GitEE·點這里

一、連接查詢

圖解示意圖

1、建表語句

部門和員工關系表：

CREATE TABLE `tb_dept` (

`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主鍵ID',

`deptName` varchar(30) DEFAULT NULL COMMENT '部門名稱',

PRIMARY KEY (`id`)

) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

CREATE TABLE `tb_emp` (

`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主鍵ID',

`empName` varchar(20) DEFAULT NULL COMMENT '員工名稱',

`deptId` int(11) DEFAULT '0' COMMENT '部門ID',

PRIMARY KEY (`id`)

) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

2、七種連接查詢

圖1：左外連接

select t1.*,t2.empName,t2.deptId

from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptId;

圖2：右外連接

select t1.*,t2.empName,t2.deptId

from tb_dept t1 RIGHT JOIN tb_emp t2 on t1.id=t2.deptId;

圖3：內連接

select t1.*,t2.empName,t2.deptId

from tb_dept t1 inner join tb_emp t2 on t1.id=t2.deptId;

圖4：左連接

查詢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;

圖5：右連接

查詢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;

圖6：全連接

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

圖7：全不連接

查詢兩張表互不關聯到的數據。

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、時間日期查詢

1、建表語句

CREATE TABLE `ms_consume` (

`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主鍵ID',

`user_id` int(11) NOT NULL COMMENT '用戶ID',

`user_name` varchar(20) NOT NULL COMMENT '用戶名',

`consume_money` decimal(20,2) DEFAULT '0.00' COMMENT '消費金額',

`create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '創建時間',

PRIMARY KEY (`id`)

) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 COMMENT='消費表';

2、日期統計案例

日期范圍內首條數據

場景：產品日常運營活動中，經常見到這樣規則：活動時間內，首筆消費滿多少，優惠多少。

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 ;

日期之間時差

場景：常用的倒計時場景

SELECT t1.*,

timestampdiff(SECOND,NOW(),t1.create_time) second_diff

FROM ms_consume t1 WHERE t1.id='9' ;

查詢今日數據

-- 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) ;

時間范圍統計

場景：統計近七日內，消費次數大于兩次的用戶。

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;

日期范圍內平均值

場景：指定日期范圍內的平均消費，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、樹形表查詢

1、建表語句

CREATE TABLE ms_city_sort (

`id` INT (11) NOT NULL AUTO_INCREMENT COMMENT '主鍵ID',

`city_name` VARCHAR (50) NOT NULL DEFAULT '' COMMENT '城市名稱',

`city_code` VARCHAR (50) NOT NULL DEFAULT '' COMMENT '城市編碼',

`parent_id` INT (11) NOT NULL DEFAULT '0' COMMENT '父級ID',

`state` INT (11) NOT NULL DEFAULT '1' COMMENT '狀態：1啟用,2停用',

`create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '創建時間',

`update_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '修改時間',

PRIMARY KEY (id)

) ENGINE = INNODB DEFAULT CHARSET = utf8 COMMENT = '城市分類管理';

2、直接SQL查詢

SELECT t1.*, t2.parentName

FROM 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、函數查詢

查詢父級名稱

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 ;

查詢根節點子級

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、源代碼地址

GitHub·地址

https://github.com/cicadasmile/mysql-data-base

GitEE·地址

https://gitee.com/cicadasmile/mysql-data-base

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