数据库MySQL/mariadb知识点——操作篇数据操作语句

Posted 2020-11-19 Welcome My blog

INSERT插入数据

单挑记录插入

INSERT INTO tb_name (col1,col2,...) VALUES (val1,val2,...);

示例：

insert into tablename(字段1名称,字段2名称,......)values(字段1值,字段2值,...)

MariaDB [testdb]> INSERT students(id,name,ages,gender) VALUES (1,\'tom\',26,\'M\');
MariaDB [testdb]> INSERT students(name,ages,gender) VALUES (\'jerry\',19,\'M\'); 
MariaDB [testdb]> INSERT students(name,ages,gender) VALUES (\'maria\',19,\'M\');
MariaDB [testdb]> INSERT students SET name=\'ouyangfeng\',ages=56,gender=\'M\';

多条记录插入

INSERT INTO tb_name (col1,col2,...) VALUES (val1,val2,...)[,(val1,val2,...),...];

MariaDB [testdb]> INSERT students(name,ages,gender) VALUES (\'xiaolongnv\',18,\'F\'),(\'dongfangbubai\',28,\'F\');

MariaDB [testdb]> SELECT * FROM students;
+----+---------------+------+--------+
| id | name          | ages | gender |
+----+---------------+------+--------+
|  1 | tom           |   26 | M      |
|  2 | jerry         |   19 | M      |
|  3 | maria         |   19 | M      |
|  4 | xiaolongnv    |   18 | F      |
|  5 | dongfangbubai |   28 | F      |
|  6 | ouyangfeng    |   56 | M      |
+----+---------------+------+--------+

 从其他表查询数据保存到此表中

MariaDB [testdb]> ALTER TABLE students ADD address TEXT;  #加个字段做测试用

MariaDB [testdb]> INSERT students(name,address) SELECT user,host FROM mysql.user;

MariaDB [testdb]> SELECT * FROM students;
+----+---------------+------+--------+-----------+
| id | name          | ages | gender | address   |
+----+---------------+------+--------+-----------+
|  1 | tom           |   26 | M      | NULL      |
|  2 | jerry         |   19 | M      | NULL      |
|  3 | maria         |   19 | M      | NULL      |
|  4 | xiaolongnv    |   18 | F      | NULL      |
|  5 | dongfangbubai |   28 | F      | NULL      |
|  6 | ouyangfeng    |   56 | M      | NULL      |
|  7 | root          |    0 | NULL   | 127.0.0.1 |
|  8 | root          |    0 | NULL   | ::1       |
|  9 |               |    0 | NULL   | centos7   |
| 10 | root          |    0 | NULL   | centos7   |
| 11 |               |    0 | NULL   | localhost |
| 12 | root          |    0 | NULL   | localhost |
+----+---------------+------+--------+-----------+

UPDATE 修改数据

UPDATE tbl_name SET col1=value1,col2=value2,... WHERE col=value;

修改数据，主要通过where字句给定修改反而，而where字句的示例可以参考select常用语句；

示例：

MariaDB [testdb]> UPDATE students SET gender=\'F\' WHERE id=3;

DELETE 删除数据

删除语句比较简单，主要是通过where字句给定删除范围，而where字句的示例可以参考select语句，删除前请确定给出条件没有任何问题，在不确定的情况下不要随意删除数据。

MariaDB [testdb]> DELETE FROM students WHERE name=\'\';  #删除名字为空的记录
MariaDB [testdb]> TRUNCATE TABLE user;  #情况表记录

注意：一定要有限制条件（WHERE | LIMIT），否则将修改所有行的指定字段

SELECT 数据查询

基础查询

1、选择

示例：

查询maria的信息

MariaDB [testdb]> SELECT * FROM students WHERE name=\'maria\';

查询2到5号学生的信息

MariaDB [testdb]> SELECT * FROM students WHERE id BETWEEN 2 AND 5;

查询jerry和xiaolongnv的信息

MariaDB [testdb]> SELECT * FROM students WHERE name IN (\'jerry\',\'xiaolongnv\');

查询年龄不为空的信息

MariaDB [testdb]> SELECT * FROM students WHERE gender IS NOT NULL;

查询姓名中包含\'o\'的信息

MariaDB [testdb]> SELECT * FROM students WHERE name LIKE \'%o%\';　

2、投影

查询时给字段添加别名

MariaDB [testdb]> SELECT user AS 用户,host AS 主机,password AS 密码 FROM mysql.user;

3、分组

示例

查询男生、女生年龄的平均值

MariaDB [testdb]> SELECT gender,AVG(ages) FROM students GROUP BY gender;

只显示男生的平均年龄信息

MariaDB [testdb]> SELECT gender,AVG(ages) FROM students GROUP BY gender HAVING gender=\'M\';

4、排序

示例

按年龄排序，倒序显示

MariaDB [testdb]> SELECT * FROM students ORDER BY ages DESC;

按年龄排序，过滤年龄大于0的，正序排序，取前三条记录

MariaDB [testdb]> SELECT * FROM students WHERE ages > 0 ORDER BY ages LIMIT 3;

5、常用参数

 1 AS：别名
 2 WHERE：指明过滤条件以实现“选择”的功能
 3 +, -, *, /, %：算术操作符
 4 =, !=, <>, >, <, >=, <=：比较操作符
 5 BETWEEN min_num AND max_num：在min_num和max_mun之间
 6 IN (element1,element2,...)：在element...中的
 7 IS NULL：为空
 8 IS NOT NULL：不为空
 9 LIKE：做匹配，像。。。
10     %：任意长度的任意字符
11     _：单个任意字符
12 RLIKE：正则表达式，不建议用
13 REGEXP：同上
14 NOT, AND, OR, XOR：逻辑操作符
15 GROUP BY：根据指定的条件把查询结果进行“分组”以用于做“聚合”运算
16 AVG() 平均数
17 MAX() 最大数
18 MIN() 最小数
19 COUNT() 统计
20 SUM() 求和
21 HAVING ：对分组聚合运算后的结果指定过滤条件。类似WHERE的作用，但只能在分组中使用
22 ORDER BY：排序
23 ASC：正序，默认
24 DESC：倒序
25 -KEYWORD：在排序时在关键字前加-可以避免把NULL排在前边
26 LIMIT [[offset,]row_count]：对查询的结果进行输出行数数量限制

参数

 

多表查询

在开始多表查询之前，我们对之前的表进行下手动扩展

MariaDB [testdb]> DELETE FROM students WHERE id BETWEEN 7 AND 12;
MariaDB [testdb]> CREATE TABLE score (id TINYINT(2) UNSIGNED AUTO_INCREMENT PRIMARY KEY,score TINYINT(3));
MariaDB [testdb]> ALTER TABLE students ADD sid TINYINT(2); 
MariaDB [testdb]> UPDATE students SET sid=6 WHERE id=6;
MariaDB [testdb]> INSERT score SET score=87;
MariaDB [testdb]> SELECT * FROM students;
+----+---------------+------+--------+---------+------+
| id | name          | ages | gender | address | sid  |
+----+---------------+------+--------+---------+------+
|  1 | tom           |   26 | M      | NULL    |    1 |
|  2 | jerry         |   19 | M      | NULL    |    2 |
|  3 | maria         |   19 | F      | NULL    |    3 |
|  4 | xiaolongnv    |   18 | F      | NULL    |    4 |
|  5 | dongfangbubai |   28 | F      | NULL    |    5 |
|  6 | ouyangfeng    |   56 | M      | NULL    |    6 |
+----+---------------+------+--------+---------+------+
MariaDB [testdb]> SELECT * FROM score;   
+----+-------+
| id | score |
+----+-------+
|  1 |    99 |
|  2 |    98 |
|  3 |    88 |
|  4 |    68 |
|  5 |    78 |
|  6 |    87 |
+----+-------+

 

 

 

1、俩张表取交集

MariaDB [testdb]> SELECT * FROM students AS s,score AS o WHERE s.sid=o.id;

2、JOIN ON：交叉连接

MariaDB [testdb]> SELECT * FROM students JOIN score;

3、INNER JOIN ON：内连接

MariaDB [testdb]> SELECT t.name,s.score FROM students AS t INNER JOIN score AS s ON t.sid=s.id;
+---------------+-------+
| name          | score |
+---------------+-------+
| tom           |    99 |
| jerry         |    98 |
| maria         |    88 |
| xiaolongnv    |    68 |
| dongfangbubai |    78 |
| ouyangfeng    |    87 |
+---------------+-------+

4、LEFT OUTER JOIN ON：左外连接

MariaDB [testdb]> SELECT t.name,s.score FROM students AS t LEFT JOIN score AS s ON t.sid=s.id;  #左外连接
+---------------+-------+
| name          | score |
+---------------+-------+
| tom           |    99 |
| jerry         |    98 |
| maria         |    88 |
| xiaolongnv    |    68 |
| dongfangbubai |    78 |
| ouyangfeng    |    87 |
+---------------+-------+

5、RIGHT OUTER JOIN ON：右外连接

MariaDB [testdb]> SELECT * FROM students AS t RIGHT JOIN score AS s ON t.sid=s.id;  #右外连接

6、UNION ON：完全外连接

MariaDB [testdb]> SELECT name,address FROM students UNION
    -> SELECT user,host FROM mysql.user;
+---------------+-----------+
| name          | address   |
+---------------+-----------+
| tom           | NULL      |
| jerry         | NULL      |
| maria         | NULL      |
| xiaolongnv    | NULL      |
| dongfangbubai | NULL      |
| ouyangfeng    | NULL      |
| root          | 127.0.0.1 |
| root          | ::1       |
|               | centos7   |
| root          | centos7   |
|               | localhost |
| root          | localhost |
+---------------+-----------+

7、自连接

MariaDB [testdb]> ALTER TABLE students ADD tid TINYINT(2);  #再加一个tid字段
MariaDB [testdb]> SELECT * FROM students;
+----+---------------+------+--------+---------+------+------+
| id | name          | ages | gender | address | sid  | tid  |
+----+---------------+------+--------+---------+------+------+
|  1 | tom           |   26 | M      | NULL    |    1 |    2 |
|  2 | jerry         |   19 | M      | NULL    |    2 |    1 |
|  3 | maria         |   19 | F      | NULL    |    3 |    4 |
|  4 | xiaolongnv    |   18 | F      | NULL    |    4 |    5 |
|  5 | dongfangbubai |   28 | F      | NULL    |    5 |    4 |
|  6 | ouyangfeng    |   56 | M      | NULL    |    6 |    4 |
+----+---------------+------+--------+---------+------+------+

MariaDB [testdb]> SELECT s1.name AS studentname,s2.name AS teachername FROM students AS s1 INNER JOIN students AS s2 ON s1.id=s2.tid;
+---------------+---------------+
| studentname   | teachername   |
+---------------+---------------+
| jerry         | tom           |
| tom           | jerry         |
| xiaolongnv    | maria         |
| dongfangbubai | xiaolongnv    |
| xiaolongnv    | dongfangbubai |
| xiaolongnv    | ouyangfeng    |
+---------------+---------------+

 

子查询

子查询：在查询语句嵌套着查询语句，性能较差，基于某语句的查询结果再次进行的查询

1、用在WHERE子句中的子查询

• 用于比较表达式中的子查询；子查询仅能返回单个值

示例：

查询大于平均年龄的同学

MariaDB [testdb]> SELECT name,ages FROM students WHERE ages > (SELECT AVG(ages) FROM students); 

• 用于IN中的子查询：子查询应该单键查询并返回一个或多个值从构成列表

2、用于FROM子句中的子查询

SELECT tb_alias.col1,... FROM (SELECT clause) AS tb_alias WHERE Clause;