MySQL/mariadb知识点——操作篇(4)数据操作语句

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

AS：别名
WHERE：指明过滤条件以实现“选择”的功能
+, -, *, /, %：算术操作符
=, !=, <>, >, <, >=, <=：比较操作符
BETWEEN min_num AND max_num：在min_num和max_mun之间
IN (element1,element2,...)：在element...中的
IS NULL：为空
IS NOT NULL：不为空
LIKE：做匹配，像。。。
    %：任意长度的任意字符
    _：单个任意字符
RLIKE：正则表达式，不建议用
REGEXP：同上
NOT, AND, OR, XOR：逻辑操作符
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
AVG() 平均数
MAX() 最大数
MIN() 最小数
COUNT() 统计
SUM() 求和
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
ORDER BY：排序
ASC：正序，默认
DESC：倒序
-KEYWORD：在排序时在关键字前加-可以避免把NULL排在前边
LIMIT [[offset,]row_count]：对查询的结果进行输出行数数量限制

 

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;