MySQL Basics (01): Classic case of practical queries, finishing summary

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First, join queries

Diagrammatic representation

1, construction of the table statement

Departments and employees table:

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 or seven join query

• Figure 1: left outer connector

select t1.*,t2.empName,t2.deptId 
from tb_dept t1 LEFT JOIN tb_emp t2 on t1.id=t2.deptId;

• Figure 2: right outer connector

select t1.*,t2.empName,t2.deptId 
from tb_dept t1 RIGHT JOIN tb_emp t2 on t1.id=t2.deptId;

• Figure 3: within the connector

select t1.*,t2.empName,t2.deptId 
from tb_dept t1 inner join tb_emp t2 on t1.id=t2.deptId;

• Figure 4: Left connector

Queries tb_dept table unique place.

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;

• Figure 5: right connection

Queries tb_emp table unique place.

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;

• Figure 6: fully connected

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

• Figure 7: Full not connected

Query two tables unrelated data.

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

Second, the date and time query

1, construction of the table statement

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, Statistics Date Case

• Date range's first data

Scene: product daily operations activities, often seen this rule: activity time, upfront spending how much, how many concessions.

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 ;

• The time difference between the date

Scene: Countdown common scene

SELECT t1.*,
       timestampdiff(SECOND,NOW(),t1.create_time) second_diff 
FROM ms_consume t1 WHERE t1.id='9' ;

• Today's data query

-- 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) ;

• Time statistics

Scene: Statistical nearly seven days, the consumer is greater than the number of times the user twice.

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;

• The average date range

Scene: the average consumption specified date range, and sorting.

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;

Third, the tree-table query

1, construction of the table statement

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, direct SQL queries

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, function queries

• Queries parent name

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 ;

• Queries root child

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 ;

Fourth, the source address

GitHub·地址
https://github.com/cicadasmile/mysql-data-base
GitEE·地址
https://gitee.com/cicadasmile/mysql-data-base