05: MySQL Advanced Search

table of Contents

1.1 GROUP BY packet using
1.2 mysql in NOW (), CURDATE (), CURTIME () using
1.3 DATEDIFF () function
1.4 DATE_FORMAT () displays the time in a different format
1.5 MySQL regex

1.1 GROUP BY grouping use

GROUP BY introduction

1. GROUP BY 语句根据一个或多个列对结果集进行分组,在分组的列上我们可以使用 COUNT, SUM, AVG,等函数。
2. 涉及到的操作符：GROUP BY，HAVING，ORDER BY，INNER JOIN，OUT JOIN，AS，UNION。

2, Group basic use

• Create a table

CREATE TABLE  user  (
   id  int(11) NOT NULL,
   name  char(10) NOT NULL DEFAULT '',
   date  datetime NOT NULL,
   singin  tinyint(4) NOT NULL DEFAULT '0' COMMENT '登录次数',
  PRIMARY KEY ( id )
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

• Inserting data into the table

INSERT INTO user VALUES 
('1', '小明', '2016-04-22 15:25:33', '1'),
('2', '小王', '2016-04-20 15:25:47', '3'), 
('3', '小丽', '2016-04-19 15:26:02', '2'), 
('4', '小王', '2016-04-07 15:26:14', '4'),
('5', '小明', '2016-04-11 15:26:40', '4'), 
('6', '小明', '2016-04-04 15:26:54', '2');

• Statistics of how many of the same name: Example 1

mysql> # SELECT name, COUNT(*) FROM   user GROUP BY name;
+------+----------+
| name | COUNT(*) |
+------+----------+
| 小丽 |        1 |
| 小明 |        3 |
| 小王 |        2 |
+------+----------+
3 rows in set (0.01 sec)

• Group by name, and then count the number of each person who is registered: Example 2 with rollup

mysql># SELECT name, SUM(singin) as singin_count FROM  user GROUP BY name WITH ROLLUP;
+------+--------------+
| name | singin_count |
+------+--------------+
| 小丽 |            2 |
| 小明 |            7 |
| 小王 |            7 |
| NULL |           16 |
+------+--------------+
4 rows in set (0.00 sec)

# WITH ROLLUP 可以实现在分组统计数据基础上再进行相同的统计（SUM,AVG,COUNT…）。
# 按姓名进行分组，再统计每个人登录的次数，其中记录 NULL 表示所有人的登录次数。

• Group by name, and then count the number of each person who is registered: Example 3 coalesce to set a name to replace NULL

mysql># SELECT coalesce(name, '总数'), SUM(singin) as singin_count FROM  user GROUP BY name WITH ROLLUP;
+------------------------+--------------+
| coalesce(name, '总数') | singin_count |
+------------------------+--------------+
| 小丽                   |            2 |
| 小明                   |            7 |
| 小王                   |            7 |
| 总数                   |           16 |
+------------------------+--------------+
4 rows in set (0.00 sec)

#1、我们可以使用 coalesce 来设置一个可以取代 NUll 的名称，coalesce 语法：
#2、select coalesce(a,b,c);
#3、参数说明：如果a==null,则选择b；如果b==null,则选择c；如果a!=null,则选择a；如果a b c 都为null ，则返回为null（没意义）。

• Packet filtering HAVING: Find the number of users logged in Example 4 is greater than 2 for all the

mysql> SELECT name, SUM(singin) as singin_count FROM  user GROUP BY name HAVING COUNT(*) >= 2;
+------+--------------+
| name | singin_count |
+------+--------------+
| 小明 |            7 |
| 小王 |            7 |
+------+--------------+
2 rows in set (0.00 sec)

• Students grouped by grade point average required subjects: Example 5

#1、创建表
create table student(
id int auto_increment,
name char(32) not null,
score int(10) not null,
course char(32) not null,
primary key (id));

#2、插入数据
insert into student(name,score,course) values('zhangsan',88,'english');
insert into student(name,score,course) values('zhangsan',98,'math');
insert into student(name,score,course) values('lisi',88,'math');

#3、查询
mysql> select *,avg(score) from student group by name;
+----+----------+-------+---------+------------+
| id | name     | score | course  | avg(score) |
+----+----------+-------+---------+------------+
|  4 | lisi     |    88 | math    |    88.0000 |
|  1 | zhangsan |    88 | english |    93.0000 |
+----+----------+-------+---------+------------+
2 rows in set (0.00 sec)

• 10 days before the user data of the same name registered users is greater than or equal to 2: Example 6

mysql># select *,count(name) from user where datediff(NOW(),date)>10 group by name having count(name)>=2;
+----+------+---------------------+--------+-------------+
| id | name | date                | singin | count(name) |
+----+------+---------------------+--------+-------------+
|  1 | 小明 | 2016-04-22 15:25:33 |      1 |           3 |
|  2 | 小王 | 2016-04-20 15:25:47 |      3 |           2 |
+----+------+---------------------+--------+-------------+
2 rows in set (0.00 sec)

# 原题：请查找商品表中最近30天至少有20天都有销售记录的商品

1.2 mysql the NOW (), CURDATE (), CURTIME () using

• Example 1: NOW (), CURDATE (), CURDATE () action

mysql> SELECT NOW(),CURDATE(),CURTIME();
+---------------------+------------+-----------+
| NOW()               | CURDATE()  | CURTIME() |
+---------------------+------------+-----------+
| 2018-03-18 16:28:16 | 2018-03-18 | 16:28:16  |
+---------------------+------------+-----------+
1 row in set (0.00 sec)

• Example 2: Define the time field is automatically added to the table

#1、创建表
CREATE TABLE goods(
id int auto_increment,
name varchar(50) NOT NULL,
date datetime NOT NULL DEFAULT NOW(),
PRIMARY KEY (id)
);

#2、插入一条数据
mysql># INSERT INTO goods(name) VALUES ('tea');   
    
#3、验证时间字段会自动插入
mysql># select * from goods;
+----+------+---------------------+
| id | name | date                |
+----+------+---------------------+
|  1 | tea  | 2018-03-18 16:37:19 |
+----+------+---------------------+
1 row in set (0.00 sec)

1.3 DATEDIFF () function

• Example 1: Returns the number of days between two dates

mysql># SELECT DATEDIFF('2008-11-30','2008-11-22') AS DiffDate;
+----------+
| DiffDate |
+----------+
|        8 |
+----------+
1 row in set (0.00 sec)

• Example 2: Query the last five days of new data

#1、创建表
CREATE TABLE goods(
id int auto_increment,
name varchar(50) NOT NULL,
date datetime NOT NULL DEFAULT NOW(),
PRIMARY KEY (id)
);

#2、插数据
INSERT INTO goods(name) VALUES ('tea1');
INSERT INTO goods(name) VALUES ('tea2');
INSERT INTO goods(name,date) VALUES ('tea3','2018-03-02 16:37:19');
INSERT INTO goods(name,date) VALUES ('tea4','2015-05-02 16:37:19');

#3、查询五天前的数据
mysql> select * from goods where datediff(NOW(),date)>5;
+----+------+---------------------+
| id | name | date                |
+----+------+---------------------+
|  3 | tea3 | 2018-03-02 16:37:19 |
|  4 | tea4 | 2015-05-02 16:37:19 |
+----+------+---------------------+
2 rows in set (0.00 sec)

#4、查询最近五天的新数据
mysql> select * from goods where datediff(NOW(),date)<5;
+----+------+---------------------+
| id | name | date                |
+----+------+---------------------+
|  1 | tea1 | 2018-03-18 16:56:42 |
|  2 | tea2 | 2018-03-18 16:56:43 |
+----+------+---------------------+
2 rows in set (0.00 sec)

1.4 DATE_FORMAT () displays the time in a different format

• Basic use DATE_FORMAT

select  
DATE_FORMAT(NOW(),'%Y-%m-%d'),
DATE_FORMAT(NOW(),'%Y-%m-%d %H:%m:%s');

+-------------------------------+----------------------------------------+
| DATE_FORMAT(NOW(),'%Y-%m-%d') | DATE_FORMAT(NOW(),'%Y-%m-%d %H:%m:%s') |
+-------------------------------+----------------------------------------+
| 2018-03-18                    | 2018-03-18 17:03:02                    |
+-------------------------------+----------------------------------------+
1 row in set (0.00 sec)

1.5 MySQL Regular Expressions

1, MySQL commonly used in regular

mode	description
^	Matches the beginning of the string. If the object is set RegExp Multiline property, also matches ^ '\ n' position after or '\ r'.
$	Matches the input end of the string. If the object is set RegExp Multiline property, $ also matches the position before the '\ n' or '\ r'.
.	Matches any single character except "\ n" is. To match include '\ n', including any character, like the use of '[. \ N]' mode.
[...]	Set of characters. Matches any character included. For example, '[abc]' matches "plain" in the 'a'.
[^...]	Negative character sets. Matches any character not included. For example, '[^ abc]' matches "plain" the 'p'.
p1-p2-p3	Matching p1, p2, or p3. For example, 'z
*	Matches the preceding subexpression zero or more times. For example, zo * matches "z" and "zoo". * Is equivalent to {0}.
+	Matches the preceding subexpression one or more times. For example, 'zo +' will match "zo" and "zoo", but can not match the "z". + Is equivalent to {1}.
{n}	n is a nonnegative integer. Matching the determined n times. For example, 'o {2}' does not match the "Bob" in the 'o', but can match the "food" in the two o.
{n,m}	m and n are non-negative integers, where n <= m. Match at least n times and match up to m times.

2, MySQL regular Application Example

    1、查找name字段中以'st'为开头的所有数据：
        mysql> SELECT name FROM person_tbl WHERE name REGEXP '^st';

    2、查找name字段中以'ok'为结尾的所有数据：
        mysql> SELECT name FROM person_tbl WHERE name REGEXP 'ok$';

    3、查找name字段中包含'mar'字符串的所有数据：
        mysql> SELECT name FROM person_tbl WHERE name REGEXP 'mar';

    4、查找name字段中以元音字符开头或以'ok'字符串结尾的所有数据：
        mysql> SELECT name FROM person_tbl WHERE name REGEXP '^[aeiou]|ok$';