7天快速掌握MySQL-DAY2
1. 导入示例数据库
---------------------------------------------
---连接到MySQL服务器并创建数据库
----------------------------------------------
mysql> CREATE DATABASE IF NOT EXISTS yiibaidb DEFAULT CHARSET utf8 COLLATE utf8_general_ci;
Query OK, 1 row affected (0.01 sec)
---------------------------------------------
---导入数据
----------------------------------------------
mysql> use yiibaidb;
Database changed
mysql> source D:/yiibaidb/yiibaidb.sql;
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
......
---------------------------------------------
---测试导入结果
----------------------------------------------
mysql> select city,phone,country from `offices`;
+---------------+------------------+-----------+
| city | phone | country |
+---------------+------------------+-----------+
| San Francisco | +1 650 219 4782 | USA |
| Boston | +1 215 837 0825 | USA |
| NYC | +1 212 555 3000 | USA |
| Paris | +33 14 723 4404 | France |
| Beijing | +86 33 224 5000 | China |
| Sydney | +61 2 9264 2451 | Australia |
| London | +44 20 7877 2041 | UK |
+---------------+------------------+-----------+
7 rows in set (0.00 sec)至此，示例数据库导入完毕。
2. 查询语句 select from
最基本的语句，意思是从那张表去查询什么数据列，可以是原表的列，也可以是聚合后的列，可以包含重复列，也可以去重，也可以只查看前几列。
-------------------------------------------
--最基本语句
------------------------------------------
mysql> select * from offices;
+------------+---------------+------------------+--------------------------+--------------+-------+-----------+------------+-----------+
| officeCode | city | phone | addressLine1 | addressLine2 | state | country | postalCode | territory |
+------------+---------------+------------------+--------------------------+--------------+-------+-----------+------------+-----------+
| 1 | San Francisco | +1 650 219 4782 | 100 Market Street | Suite 300 | CA | USA | 94080 | NA |
| 2 | Boston | +1 215 837 0825 | 1550 Court Place | Suite 102 | MA | USA | 02107 | NA |
| 3 | NYC | +1 212 555 3000 | 523 East 53rd Street | apt. 5A | NY | USA | 10022 | NA |
| 4 | Paris | +33 14 723 4404 | 43 Rue Jouffroy D'abbans | NULL | NULL | France | 75017 | EMEA |
| 5 | Beijing | +86 33 224 5000 | 4-1 Haidian Area | NULL | BJ | China | 110000 | NA |
| 6 | Sydney | +61 2 9264 2451 | 5-11 Wentworth Avenue | Floor #2 | NULL | Australia | NSW 2010 | APAC |
| 7 | London | +44 20 7877 2041 | 25 Old Broad Street | Level 7 | NULL | UK | EC2N 1HN | EMEA |
+------------+---------------+------------------+--------------------------+--------------+-------+-----------+------------+-----------+
7 rows in set (0.00 sec)
------------------------------------------------------------
--查看yiibaidb数据库中的table
------------------------------------------------------------
mysql> show tables;
+--------------------+
| Tables_in_yiibaidb |
+--------------------+
| customers |
| employees |
| items |
| offices |
| orderdetails |
| orders |
| payments |
| productlines |
| products |
| tokens |
+--------------------+
10 rows in set (0.00 sec)
----------------------------------------------------------
---账单表payments应该包含重复数据，首先查看行数
----------------------------------------------------------
mysql> select count(1) from payments;
+----------+
| count(1) |
+----------+
| 273 |
+----------+
1 row in set (0.00 sec)
----------------------------------------------------------
--查看payments数据表的结构
----------------------------------------------------------
mysql> describe payments;
+----------------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+---------------+------+-----+---------+-------+
| customerNumber | int(11) | NO | PRI | NULL | |
| checkNumber | varchar(50) | NO | PRI | NULL | |
| paymentDate | date | NO | | NULL | |
| amount | decimal(10,2) | NO | | NULL | |
+----------------+---------------+------+-----+---------+-------+
4 rows in set (0.01 sec)
----------------------------------------------------------
--查询非重复数据customerNumber记录条目数
----------------------------------------------------------
mysql> select count(distinct customerNumber) dis_customerNumber_count from payments;
+--------------------------+
| dis_customerNumber_count |
+--------------------------+
| 98 |
+--------------------------+
1 row in set (0.00 sec)
----------------------------------------------------------
--查询payments数据表的前10行
----------------------------------------------------------
mysql> select * from payments limit 10;
+----------------+-------------+-------------+----------+
| customerNumber | checkNumber | paymentDate | amount |
+----------------+-------------+-------------+----------+
| 103 | HQ336336 | 2014-10-19 | 6066.78 |
| 103 | JM555205 | 2013-06-05 | 14571.44 |
| 103 | OM314933 | 2014-12-18 | 1676.14 |
| 112 | BO864823 | 2014-12-17 | 14191.12 |
| 112 | HQ55022 | 2013-06-06 | 32641.98 |
| 112 | ND748579 | 2014-08-20 | 33347.88 |
| 114 | GG31455 | 2013-05-20 | 45864.03 |
| 114 | MA765515 | 2014-12-15 | 82261.22 |
| 114 | NP603840 | 2013-05-31 | 7565.08 |
| 114 | NR27552 | 2014-03-10 | 44894.74 |
+----------------+-------------+-------------+----------+
10 rows in set (0.00 sec)3. 限制条件&分组： where/group by/having
用来限制查询条件
----------------------------------------------------------
--查询payments消费额大于80000的订单记录
----------------------------------------------------------
mysql> select * from payments where amount > 80000;
+----------------+-------------+-------------+-----------+
| customerNumber | checkNumber | paymentDate | amount |
+----------------+-------------+-------------+-----------+
| 114 | MA765515 | 2014-12-15 | 82261.22 |
| 124 | AE215433 | 2015-03-05 | 101244.59 |
| 124 | BG255406 | 2014-08-28 | 85410.87 |
| 124 | ET64396 | 2015-04-16 | 83598.04 |
| 124 | KI131716 | 2013-08-15 | 111654.40 |
| 141 | ID10962 | 2014-12-31 | 116208.40 |
| 141 | JE105477 | 2015-03-18 | 120166.58 |
| 148 | KM172879 | 2013-12-26 | 105743.00 |
| 167 | GN228846 | 2013-12-03 | 85024.46 |
| 239 | NQ865547 | 2014-03-15 | 80375.24 |
| 321 | DJ15149 | 2013-11-03 | 85559.12 |
+----------------+-------------+-------------+-----------+
11 rows in set (0.00 sec)
----------------------------------------------------------
--查询消费额大于80000的订单记录中的非重复的customerNumber
----------------------------------------------------------
mysql> select customerNumber from payments where amount > 80000
-> group by customerNumber;
+----------------+
| customerNumber |
+----------------+
| 114 |
| 124 |
| 141 |
| 148 |
| 167 |
| 239 |
| 321 |
+----------------+
7 rows in set (0.00 sec)
----------------------------------------------------------------------------
--查询payments消费总额大于200000的订单记录，注意，这里是消费总额，是
--聚合后的量，需要使用having
----------------------------------------------------------------------------
mysql> select customerNumber, sum(amount) as sum_amount
-> from payments
-> group by customerNumber
-> having sum_amount > 200000;
+----------------+------------+
| customerNumber | sum_amount |
+----------------+------------+
| 124 | 584188.24 |
| 141 | 715738.98 |
+----------------+------------+
2 rows in set (0.00 sec)4. 排序函数 order by
用来排序，默认升序，desc降序，asc显示声明升序。
----------------------------------------------------------
--查询消费额最小的10个订单，从小到大
----------------------------------------------------------
mysql> select * from payments
-> order by amount
-> limit 10;
+----------------+-------------+-------------+---------+
| customerNumber | checkNumber | paymentDate | amount |
+----------------+-------------+-------------+---------+
| 398 | JPMR4544 | 2015-05-18 | 615.45 |
| 381 | MS154481 | 2013-08-22 | 1128.20 |
| 121 | FD317790 | 2013-10-28 | 1491.38 |
| 381 | CC475233 | 2013-04-19 | 1627.56 |
| 103 | OM314933 | 2014-12-18 | 1676.14 |
| 456 | MO743231 | 2014-04-30 | 1679.92 |
| 350 | OB648482 | 2015-01-29 | 1834.56 |
| 172 | AD832091 | 2014-09-09 | 1960.80 |
| 161 | BR352384 | 2014-11-14 | 2434.25 |
| 148 | DD635282 | 2014-08-11 | 2611.84 |
+----------------+-------------+-------------+---------+
10 rows in set (0.00 sec)
----------------------------------------------------------
--查询消费额最大的10个订单，从大到小
----------------------------------------------------------
mysql> select * from payments
-> order by amount desc
-> limit 10;
+----------------+-------------+-------------+-----------+
| customerNumber | checkNumber | paymentDate | amount |
+----------------+-------------+-------------+-----------+
| 141 | JE105477 | 2015-03-18 | 120166.58 |
| 141 | ID10962 | 2014-12-31 | 116208.40 |
| 124 | KI131716 | 2013-08-15 | 111654.40 |
| 148 | KM172879 | 2013-12-26 | 105743.00 |
| 124 | AE215433 | 2015-03-05 | 101244.59 |
| 321 | DJ15149 | 2013-11-03 | 85559.12 |
| 124 | BG255406 | 2014-08-28 | 85410.87 |
| 167 | GN228846 | 2013-12-03 | 85024.46 |
| 124 | ET64396 | 2015-04-16 | 83598.04 |
| 114 | MA765515 | 2014-12-15 | 82261.22 |
+----------------+-------------+-------------+-----------+
10 rows in set (0.00 sec)5. 函数
5.1 时间函数
--获取当前时间
mysql> select now();
+---------------------+
| now() |
+---------------------+
| 2019-02-27 21:18:21 |
+---------------------+
1 row in set (0.00 sec)
--时间格式转换
mysql> select date_format('2008-08-08 22:23:01', '%Y%m%d%H%i%s');
+----------------------------------------------------+
| date_format('2008-08-08 22:23:01', '%Y%m%d%H%i%s') |
+----------------------------------------------------+
| 20080808222301 |
+----------------------------------------------------+
1 row in set (0.00 sec)
mysql> select str_to_date('08/09/2008', '%m/%d/%Y'); -- 2008-08-09
+---------------------------------------+
| str_to_date('08/09/2008', '%m/%d/%Y') |
+---------------------------------------+
| 2008-08-09 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select str_to_date('08/09/08' , '%m/%d/%y'); -- 2008-08-09
+--------------------------------------+
| str_to_date('08/09/08' , '%m/%d/%y') |
+--------------------------------------+
| 2008-08-09 |
+--------------------------------------+
1 row in set (0.00 sec)
mysql> select str_to_date('08.09.2008', '%m.%d.%Y'); -- 2008-08-09
+---------------------------------------+
| str_to_date('08.09.2008', '%m.%d.%Y') |
+---------------------------------------+
| 2008-08-09 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select str_to_date('08:09:30', '%h:%i:%s'); -- 08:09:30
+-------------------------------------+
| str_to_date('08:09:30', '%h:%i:%s') |
+-------------------------------------+
| 08:09:30 |
+-------------------------------------+
1 row in set (0.00 sec)
mysql> select str_to_date('08.09.2008 08:09:30', '%m.%d.%Y %h:%i:%s'); -- 2008-08-09 08:09:30
+---------------------------------------------------------+
| str_to_date('08.09.2008 08:09:30', '%m.%d.%Y %h:%i:%s') |
+---------------------------------------------------------+
| 2008-08-09 08:09:30 |
+---------------------------------------------------------+
1 row in set (0.00 sec)
--UNIX时间戳转换为时间
mysql> select from_unixtime(1550937600);
+---------------------------+
| from_unixtime(1550937600) |
+---------------------------+
| 2019-02-24 00:00:00 |
+---------------------------+
1 row in set (0.00 sec)5.2 数值函数
--举例：产生 0～100 内的任意随机整数
mysql> select ceil(100*rand()),ceil(100*rand());
+------------------+------------------+
| ceil(100*rand()) | ceil(100*rand()) |
+------------------+------------------+
| 23 | 10 |
+------------------+------------------+
1 row in set (0.00 sec)5.3 字符串函数
--举例：CONCAT_WS(separator,str1,str2,...)：将多个字符串参数以给定的分隔符separator首尾相连后返回
mysql> select concat_ws(';','First name','Second name','Last name');
+-------------------------------------------------------+
| concat_ws(';','First name','Second name','Last name') |
+-------------------------------------------------------+
| First name;Second name;Last name |
+-------------------------------------------------------+
1 row in set (0.00 sec)6. 作业
6.1 项目一：查找重复的电子邮箱（难度：简单）
查找重复的电子邮箱（难度：简单）
创建 email表，并插入如下三行数据
+----+---------+
| Id | Email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
| 3 | a@b.com |
+----+---------+
编写一个 SQL 查询，查找 email 表中所有重复的电子邮箱。
根据以上输入，你的查询应返回以下结果：
+---------+
| Email |
+---------+
| a@b.com |
+---------+
说明：所有电子邮箱都是小写字母。
附录：
-- 创建表
CREATE TABLE email (
ID INT NOT NULL PRIMARY KEY,
Email VARCHAR(255)
)
-- 插入数据
INSERT INTO email VALUES(1, 'a@b.com');
INSERT INTO email VALUES(2, 'c@d.com');
INSERT INTO email VALUES(3, 'a@b.com');请尝试写出sql查询出重复的电子邮箱。
6.2 项目二：查找大国（难度：简单）
创建如下 World 表
+-----------------+------------+------------+--------------+---------------+
| name | continent | area | population | gdp |
+-----------------+------------+------------+--------------+---------------+
| Afghanistan | Asia | 652230 | 25500100 | 20343000 |
| Albania | Europe | 28748 | 2831741 | 12960000 |
| Algeria | Africa | 2381741 | 37100000 | 188681000 |
| Andorra | Europe | 468 | 78115 | 3712000 |
| Angola | Africa | 1246700 | 20609294 | 100990000 |
+-----------------+------------+------------+--------------+---------------+
如果一个国家的面积超过300万平方公里，或者(人口超过2500万并且gdp超过2000万)，
那么这个国家就是大国家。
编写一个SQL查询，输出表中所有大国家的名称、人口和面积。
例如，根据上表，我们应该输出:
+--------------+-------------+--------------+
| name | population | area |
+--------------+-------------+--------------+
| Afghanistan | 25500100 | 652230 |
| Algeria | 37100000 | 2381741 |
+--------------+-------------+--------------+
附录：
-- 创建表
CREATE TABLE World (
name VARCHAR(50) NOT NULL PRIMARY KEY,
continent VARCHAR(50) NOT NULL,
area INT NOT NULL,
population INT NOT NULL,
gdp INT NOT NULL
);
-- 插入数据
INSERT INTO World VALUES( 'Afghanistan', 'Asia',652230,25500100,20343000);
INSERT INTO World VALUES( 'Albania', 'Europe' ,28748,2831741,12960000);
INSERT INTO World VALUES( 'Algeria', 'Africa' ,2381741,37100000,188681000);
INSERT INTO World VALUES( 'Andorra' , 'Europe' ,468,78115,3712000);
INSERT INTO World VALUES( 'Angola' , 'Africa' ,1246700,20609294,100990000);请尝试写出sql查询大国家的名称、人口和面积。
如果喜欢，就给个好看吧~~
本文参与 腾讯云自媒体同步曝光计划，分享自微信公众号。
原始发表：2019-03-08，如有侵权请联系 cloudcommunity@tencent.com 删除
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