MySQL的基本操作

技术2022-07-10 127

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

MySQL的基本操作(针对小白2）前言创建和使用数据库创建,查看，选择和删除数据库展示，创建和删除表格将数据加载到表中，表中数据全清空和特定行的清空从表中检索信息选择所有数据选择特定行选择特定列排序行日期计算模式匹配计数行获取有关数据库和表的信息结束语

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;

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;

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;

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> 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> 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;

选择特定行

使用AND 逻辑运算符

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

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

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_

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

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;

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;

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