mysql 基本操作二

1.查询数据

MariaDB [jason]> select * from runoob_tbl limit  offset ;

默认是从偏移量为0 处开始查村数据，通过指定offset 可以从offset 处开始取数

2.where 语句

MariaDB [jason]> select * from runoob_tbl where runoob_title like '%python%';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习python   | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> select * from runoob_tbl where runoob_title like '%Python%';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习python   | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)

mysql where 条件不区分大小写，若要区分大小写则采用下面的写法

MariaDB [jason]> select * from runoob_tbl where binary runoob_title like '%Python%';
Empty set (0.00 sec)
 
MariaDB [jason]> select * from runoob_tbl where binary runoob_title like '%python%';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习python   | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)

3.update  更新表记录

MariaDB [jason]> update runoob_tbl set runoob_title='java', runoob_author ='jason' where runoob_id = ;
ERROR  (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:
Current database: jason
 
Query OK,  row affected (0.04 sec)
Rows matched:   Changed:   Warnings: 
 
MariaDB [jason]> select * from runoob_tbl;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | java         | jason         | --      |
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习scala    | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+

4.删除表记录 delete

delete 语句如果不指定where 条件则会删除表内所有数据

MariaDB [jason]> delete from runoob_tbl where runoob_id = ;
Query OK,  row affected (0.00 sec)
 
MariaDB [jason]> select * from runoob_tbl;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习scala    | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> delete from runoob_tbl;
Query OK,  rows affected (0.00 sec)
 
MariaDB [jason]> select * from runoob_tbl;
Empty set (0.00 sec)

5.like 语句

MariaDB [jason]> select * from runoob_tbl where runoob_title like '%python';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+

6.union and union all

MariaDB [jason]> select runoob_title as a from runoob_tbl union all select runoob_author as a from runoob_tbl order by a;
+--------------+
| a            |
+--------------+
| dong         |
| jason        |
| 学习java     |
| 学习linux    |
| 学习python   |
| 学习scala    |
| 菜鸟教程     |
| 菜鸟教程     |
+--------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> select runoob_title from runoob_tbl union all select runoob_author from runoob_tbl;
+--------------+
| runoob_title |
+--------------+
| 学习python   |
| 学习scala    |
| 学习java     |
| 学习linux    |
| 菜鸟教程     |
| 菜鸟教程     |
| jason        |
| dong         |
+--------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> select runoob_title from runoob_tbl union  select runoob_author from runoob_tbl;
+--------------+
| runoob_title |
+--------------+
| 学习python   |
| 学习scala    |
| 学习java     |
| 学习linux    |
| 菜鸟教程     |
| jason        |
| dong         |
+--------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> select runoob_title from runoob_tbl union distinct select runoob_author from runoob_tbl;
+--------------+
| runoob_title |
+--------------+
| 学习python   |
| 学习scala    |
| 学习java     |
| 学习linux    |
| 菜鸟教程     |
| jason        |
| dong         |
+--------------+
 rows in set (0.00 sec)

union 与 union distinct 功能相同，会把union 后的结果去重，union all 则不去重。

如果有order 则order 是对全局结果的排序

MariaDB [jason]> select runoob_title from runoob_tbl union all select runoob_author from runoob_tbl order by runoob_author;
ERROR  (42S22): Unknown column 'runoob_author' in 'order clause'
MariaDB [jason]> select runoob_title as a from runoob_tbl union all select runoob_author as a from runoob_tbl order by a;
+--------------+
| a            |
+--------------+
| dong         |
| jason        |
| 学习java     |
| 学习linux    |
| 学习python   |
| 学习scala    |
| 菜鸟教程     |
| 菜鸟教程     |
+--------------+
 rows in set (0.00 sec)

7.排序 order by

MariaDB [jason]> select * from runoob_tbl order by runoob_id asc;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习java     | jason         | --      |
|          | 学习linux    | dong          | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.01 sec)
 
MariaDB [jason]> select * from runoob_tbl order by runoob_id desc;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习linux    | dong          | --      |
|          | 学习java     | jason         | --      |
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习python   | 菜鸟教程      | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)

8.group by

group by 可以用于sum，count，avg 等聚合函数

首先看一下要操作的表中的数据

MariaDB [jason]> select * from employee_tbl;
+----+--------+---------------------+--------+
| id | name   | date                | singin |
+----+--------+---------------------+--------+
|   | 小明   | -- :: |       |
|   | 小王   | -- :: |       |
|   | 小丽   | -- :: |       |
|   | 小王   | -- :: |       |
|   | 小明   | -- :: |       |
|   | 小明   | -- :: |       |
+----+--------+---------------------+--------+
 rows in set (0.00 sec)

MariaDB [jason]> select name,count(*) from employee_tbl group by name;
+--------+----------+
| name   | count(*) |
+--------+----------+
| 小丽   |         |
| 小明   |         |
| 小王   |         |
+--------+----------+
 rows in set (0.00 sec)

with rollup 可以实现再分组统计数据的基础之上再进行相同的统计

MariaDB [jason]> select name,sum(singin) from employee_tbl group by name with rollup;
+--------+-------------+
| name   | sum(singin) |
+--------+-------------+
| 小丽   |            |
| 小明   |            |
| 小王   |            |
| NULL   |           |
+--------+-------------+
 rows in set (0.00 sec)

但是最后一行的name 为null ，我们可以用coalesce 为其赋值，

coalesce（name,'总数'）,如果name 为null 则用 ‘总数’ 来命名

MariaDB [jason]> select coalesce(name,'总数'),sum(singin) from employee_tbl group by name with rollup;
+-------------------------+-------------+
| coalesce(name,'总数')   | sum(singin) |
+-------------------------+-------------+
| 小丽                    |            |
| 小明                    |            |
| 小王                    |            |
| 总数                    |           |
+-------------------------+-------------+
 rows in set (0.00 sec)

9.join

MariaDB [jason]> select *  from runoob_tbl a  join employee_tbl  b on a.runoob_id=b.id;
+-----------+--------------+---------------+-----------------+----+--------+---------------------+--------+
| runoob_id | runoob_title | runoob_author | submission_date | id | name   | date                | singin |
+-----------+--------------+---------------+-----------------+----+--------+---------------------+--------+
|          | 学习python   | 菜鸟教程      | --      |   | 小明   | -- :: |       |
|          | 学习scala    | 菜鸟教程      | --      |   | 小王   | -- :: |       |
|          | 学习java     | jason         | --      |   | 小丽   | -- :: |       |
|          | 学习linux    | dong          | --      |   | 小王   | -- :: |       |
+-----------+--------------+---------------+-----------------+----+--------+---------------------+--------+
 rows in set (0.00 sec)

MariaDB [jason]> select *  from runoob_tbl a left join employee_tbl  b on a.runoob_id=b.id;
+-----------+--------------+---------------+-----------------+------+--------+---------------------+--------+
| runoob_id | runoob_title | runoob_author | submission_date | id   | name   | date                | singin |
+-----------+--------------+---------------+-----------------+------+--------+---------------------+--------+
|          | 学习python   | 菜鸟教程      | --      |     | 小明   | -- :: |       |
|          | 学习scala    | 菜鸟教程      | --      |     | 小王   | -- :: |       |
|          | 学习java     | jason         | --      |     | 小丽   | -- :: |       |
|          | 学习linux    | dong          | --      |     | 小王   | -- :: |       |
+-----------+--------------+---------------+-----------------+------+--------+---------------------+--------+
 rows in set (0.00 sec)

MariaDB [jason]> select *  from runoob_tbl a right join employee_tbl  b on a.runoob_id=b.id;
+-----------+--------------+---------------+-----------------+----+--------+---------------------+--------+
| runoob_id | runoob_title | runoob_author | submission_date | id | name   | date                | singin |
+-----------+--------------+---------------+-----------------+----+--------+---------------------+--------+
|          | 学习python   | 菜鸟教程      | --      |   | 小明   | -- :: |       |
|          | 学习scala    | 菜鸟教程      | --      |   | 小王   | -- :: |       |
|          | 学习java     | jason         | --      |   | 小丽   | -- :: |       |
|          | 学习linux    | dong          | --      |   | 小王   | -- :: |       |
|      NULL | NULL         | NULL          | NULL            |   | 小明   | -- :: |       |
|      NULL | NULL         | NULL          | NULL            |   | 小明   | -- :: |       |
+-----------+--------------+---------------+-----------------+----+--------+---------------------+--------+
 rows in set (0.00 sec)

10. null 值的处理

mysql 中判断值是否为null 不能用 = null，<> null, 要用 is null  或者is not null, null = null 返回false ，null 与任何值的比较都是false，null 值的比较要用 <=>,null <=> null返回true

11. mysql 中的正则表达式

12.事务

• 在 MySQL 中只有使用了 Innodb 数据库引擎的数据库或表才支持事务。
• 事务处理可以用来维护数据库的完整性，保证成批的 SQL 语句要么全部执行，要么全部不执行。
• 事务用来管理 insert,update,delete 语句

MariaDB [jason]> begin;
Query OK,  rows affected (0.00 sec)
 
MariaDB [jason]> insert into runoob_tbl(
    -> runoob_title,runoob_author,submission_date
    -> )
    -> values
    -> ("学习php","jason",now()),
    -> ("学习c++","dong",now());
Query OK,  rows affected,  warnings (0.01 sec)
Records:   Duplicates:   Warnings: 
 
MariaDB [jason]> select * from runoob_tbl ;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习java     | jason         | --      |
|          | 学习linux    | dong          | --      |
|          | 学习php      | jason         | --      |
|          | 学习c++      | dong          | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> rollback;
Query OK,  rows affected (0.00 sec)
 
MariaDB [jason]> select * from runoob_tbl ;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习java     | jason         | --      |
|          | 学习linux    | dong          | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)
 
MariaDB [jason]> insert into runoob_tbl(
    -> runoob_title,runoob_author,submission_date
    -> )
    -> values
    -> ("学习php","jason",now()),
    -> ("学习c++","dong",now());
Query OK,  rows affected,  warnings (0.01 sec)
Records:   Duplicates:   Warnings: 
 
MariaDB [jason]> commit;
Query OK,  rows affected (0.00 sec)
 
MariaDB [jason]> select * from runoob_tbl ;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|          | 学习python   | 菜鸟教程      | --      |
|          | 学习scala    | 菜鸟教程      | --      |
|          | 学习java     | jason         | --      |
|          | 学习linux    | dong          | --      |
|          | 学习php      | jason         | --      |
|          | 学习c++      | dong          | --      |
+-----------+--------------+---------------+-----------------+
 rows in set (0.00 sec)