MySQL的基本操作
前言
内容有点多，建议收藏起来再看。
这次学习和分享的部分是MySQL8.0官方文档的第三章里的创建和使用数据库和常见查询示例，地址是：
https://dev.mysql.com/doc/refman/8.0/en/tutorial.html
OK，上正文。也可以直接通过目录进行跳转哦
目录
创建和使用数据库
创建,查看，选择和删除数据库
创建数据库：CREATE DATABASE XXX;
mysql> CREATE DATABASE menagerie; Query OK, 1 row affected (0.01 sec)查看数据库：SHOW DATABASES;
mysql> SHOW DATABASES; +--------------------+ | Database | +--------------------+ | information_schema | | menagerie | | mysql | | performance_schema | | sys | +--------------------+ 5 rows in set (0.00 sec)使用数据库：USE XXX
mysql> USE menagerie Database changed删除数据库：DROP DATABASE XXX
mysql> DROP DATABASE menagerie; Query OK, 0 rows affected (0.00 sec)展示，创建和删除表格
在上面的USE menagerie之后哈
展示库里的表：SHOW TABLES;mysql> SHOW TABLES; Empty set (0.00 sec)创建表：CREATE TABLE XXX（。。。）
如
CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20), species VARCHAR(20), sex CHAR(1), birth DATE, death DATE); Query OK, 0 rows affected (0.00 sec)上面代码的意思是：表被命名为pet，包含的列有六个，分别是name,owner,species,sex,birth,death。数据类型分别为VARCHAR(20)，VARCHAR(20)，VARCHAR(20)，CHAR(1)，DATE，DATE。
接着再次展示库里的表，结果如图
获取有关表结构或查询执行计划的信息：DESCRIBE XXX;mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+ 6 rows in set (0.00 sec)展示的信息即为每一列的信息
删除那个表：DROP TABLE XXX;mysql> DROP TABLE pet; Query OK, 0 rows affected (0.01 sec)将数据加载到表中，表中数据全清空和特定行的清空
将新行插入到现有表中：INSERT
INSERT INTO pet VALUES ('Puffball','Diane','hamster','f','1999-03-30',NULL);意思是往pet这个表里插入’Puffball’,‘Diane’,‘hamster’,‘f’,‘1999-03-30’,NULL数据。
检索这个表的全部信息：SELECT * FROM XXX;mysql> select * from pet; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+-------+---------+------+------------+-------+ 1 row in set (0.00 sec)说明(‘Puffball’,‘Diane’,‘hamster’,‘f’,‘1999-03-30’,NULL)这个数据已经加载进pet这个表中。
表中数据清空：TRUNCATE TABLE XXX;mysql> select * from pet; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+-------+---------+------+------------+-------+ 1 row in set (0.00 sec)
mysql> TRUNCATE TABLE pet;
Query OK, 0 rows affected (0.02 sec)
mysql> select * from pet;
Empty set (0.00 sec)
清空表中某行数据：DELETE FROM XXX where XXX = “XXX”;
mysql> select * from pet; +----------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+-------+
| Puffball | Diane | hamster | f | 1999-03-30 | NULL |
+----------+-------+---------+------+------------+-------+
1 row in set (0.00 sec)
mysql> DELETE FROM pet where name = “Puffball”;
Query OK, 1 row affected (0.01 sec)
mysql> select * from pet;
Empty set (0.00 sec)
从表中检索信息
检索用的是SELECT
学习这步操作之前先输入以下命令
INSERT INTO pet VALUES ('Fluffy','Harold','cat','f','1993-02-04',NULL); INSERT INTO pet VALUES ('Claws','Gwen','cat','m','1994-03-17', NULL); INSERT INTO pet VALUES ('Buffy','Harold','dog','f','1989-05-13',NULL); INSERT INTO pet VALUES ('Fang','Benny','dog','m','1990-08-27',NULL); INSERT INTO pet VALUES ('Bowser','Diane','dog','m','1979-08-31','1995-07-29'); INSERT INTO pet VALUES ('Chirpy','Gwen','bird','f','1998-09-11',NULL); INSERT INTO pet VALUES ('Slim','Benny','snake','m','1996-04-29',NULL); INSERT INTO pet VALUES ('Puffball','Diane','hamster','f','1999-03-30',NULL);从而使得pet这个表是这个样子
mysql> select * from pet; +----------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+--------+---------+------+------------+------------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Fang | Benny | dog | m | 1990-08-27 | NULL | | Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 | | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+--------+---------+------+------------+------------+ 8 rows in set (0.00 sec)选择所有数据
select * from XXX;
mysql> select * from pet; +----------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+--------+---------+------+------------+------------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Fang | Benny | dog | m | 1990-08-27 | NULL | | Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 | | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+--------+---------+------+------------+------------+ 8 rows in set (0.00 sec)选择特定行
mysql> SELECT * FROM pet WHERE name = 'Bowser'; +--------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+-------+---------+------+------------+------------+ | Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 | +--------+-------+---------+------+------------+------------+ 1 row in set (0.00 sec)mysql> SELECT * FROM pet WHERE birth >= '1998-1-1'; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+-------+---------+------+------------+-------+ 2 rows in set (0.00 sec)使用AND 逻辑运算符
mysql> SELECT * FROM pet WHERE species = 'snake' OR species = 'bird'; +--------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | +--------+-------+---------+------+------------+-------+ 2 rows in set (0.00 sec)AND和OR可以混合使用，尽管 AND优先级高于 OR。如果同时使用这两个运算符，则最好使用括号来明确指示应如何对条件进行分组
mysql> SELECT * FROM pet WHERE (species = 'cat' AND sex = 'm') -> OR (species = 'dog' AND sex = 'f'); +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+ 2 rows in set (0.00 sec)
选择特定列
mysql> SELECT name, birth FROM pet;
+----------+------------+
| name | birth |
+----------+------------+
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| Buffy | 1989-05-13 |
| Fang | 1990-08-27 |
| Bowser | 1979-08-31 |
| Chirpy | 1998-09-11 |
| Slim | 1996-04-29 |
| Puffball | 1999-03-30 |
+----------+------------+
8 rows in set (0.00 sec)
结合选取特定行的特定列
mysql> SELECT name, species, birth FROM pet
-> WHERE species = 'dog' OR species = 'cat';
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Fluffy | cat | 1993-02-04 |
| Claws | cat | 1994-03-17 |
| Buffy | dog | 1989-05-13 |
| Fang | dog | 1990-08-27 |
| Bowser | dog | 1979-08-31 |
+--------+---------+------------+
5 rows in set (0.01 sec)
排序行
使用ORDER BY子句
mysql> SELECT name, birth FROM pet ORDER BY birth;
+----------+------------+
| name | birth |
+----------+------------+
| Bowser | 1979-08-31 |
| Buffy | 1989-05-13 |
| Fang | 1990-08-27 |
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| Slim | 1996-04-29 |
| Chirpy | 1998-09-11 |
| Puffball | 1999-03-30 |
+----------+------------+
8 rows in set (0.00 sec)
默认的排序顺序是升序，先是最小值。要以倒序（降序）排序，请将DESC关键字添加到要排序的列的名称上
mysql> SELECT name, birth FROM pet ORDER BY birth DESC;
+----------+------------+
| name | birth |
+----------+------------+
| Puffball | 1999-03-30 |
| Chirpy | 1998-09-11 |
| Slim | 1996-04-29 |
| Claws | 1994-03-17 |
| Fluffy | 1993-02-04 |
| Fang | 1990-08-27 |
| Buffy | 1989-05-13 |
| Bowser | 1979-08-31 |
+----------+------------+
8 rows in set (0.00 sec)
日期计算
请使用该 TIMESTAMPDIFF()功能。它的参数是要表示结果的单位，以及两个日期之间的差值。
mysql> SELECT name, birth, CURDATE(), -> TIMESTAMPDIFF(YEAR,birth,CURDATE()) AS age -> FROM pet; +----------+------------+------------+------+ | name | birth | CURDATE() | age | +----------+------------+------------+------+ | Fluffy | 1993-02-04 | 2020-04-15 | 27 | | Claws | 1994-03-17 | 2020-04-15 | 26 | | Buffy | 1989-05-13 | 2020-04-15 | 30 | | Fang | 1990-08-27 | 2020-04-15 | 29 | | Bowser | 1979-08-31 | 2020-04-15 | 40 | | Chirpy | 1998-09-11 | 2020-04-15 | 21 | | Slim | 1996-04-29 | 2020-04-15 | 23 | | Puffball | 1999-03-30 | 2020-04-15 | 21 | +----------+------------+------------+------+ 8 rows in set (0.01 sec)模式匹配
MySQL提供了标准的SQL模式匹配以及基于扩展的正则表达式的模式匹配形式，该正则表达式类似于vi，grep和 sed之类的Unix实用程序使用的扩展正则表达式 。
查找以b开头的name：mysql> SELECT * FROM pet WHERE name LIKE 'b%'; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+ 2 rows in set (0.00 sec)查找以fy结尾的name
mysql> SELECT * FROM pet WHERE name LIKE '%fy'; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+ 2 rows in set (0.00 sec)查找包含w的name
mysql> SELECT * FROM pet WHERE name LIKE '%w%'; +--------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 | +--------+-------+---------+------+------------+------------+ 2 rows in set (0.00 sec)
查找正好包含五个字符的名称，使用_
mysql> SELECT * FROM pet WHERE name LIKE '_____';
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
2 rows in set (0.00 sec)
计数行
COUNT(*)计算行数
计算pet表中有多少行
mysql> SELECT COUNT(*) FROM pet;
+----------+
| COUNT(*) |
+----------+
| 8 |
+----------+
1 row in set (0.01 sec)
如果要找出每个主人有多少只宠物
mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;
+--------+----------+
| owner | COUNT(*) |
+--------+----------+
| Harold | 2 |
| Gwen | 2 |
| Benny | 2 |
| Diane | 2 |
+--------+----------+
4 rows in set (0.00 sec)
每个动物的种类的数量：
mysql> SELECT species, COUNT(*) FROM pet GROUP BY species;
+---------+----------+
| species | COUNT(*) |
+---------+----------+
| cat | 2 |
| dog | 3 |
| bird | 1 |
| snake | 1 |
| hamster | 1 |
+---------+----------+
5 rows in set (0.00 sec)
每个动物和性别组合的数量：
mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| dog | m | 2 |
| bird | f | 1 |
| snake | m | 1 |
| hamster | f | 1 |
+---------+------+----------+
7 rows in set (0.00 sec)
仅对狗和猫执行的前一个查询（每个动物和性别组合的数量）
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE species = 'dog' OR species = 'cat'
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| dog | m | 2 |
+---------+------+----------+
4 rows in set (0.00 sec)
获取有关数据库和表的信息
使用
SHOW或SELECT或DESCRIBE
SHOW DATABASES;
mysql> SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| information_schema |
| menagerie |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
SELECT DATABASE();
mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| menagerie |
+------------+
1 row in set (0.00 sec)
SHOW TABLES;
mysql> SHOW TABLES;
+---------------------+
| Tables_in_menagerie |
+---------------------+
| pet |
+---------------------+
1 row in set (0.01 sec)
DESCRIBE pet;
mysql> DESCRIBE pet;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| owner | varchar(20) | YES | | NULL | |
| species | varchar(20) | YES | | NULL | |
| sex | char(1) | YES | | NULL | |
| birth | date | YES | | NULL | |
| death | date | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
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