mysql基础操作整理(一)

显示当前数据库

mysql> select database();
+------------+
| database() |
+------------+
| test       |
+------------+
 row in set (0.00 sec)

显示数据库表

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t1             |
+----------------+
 row in set (0.00 sec)

mysql表复制

//复制表结构
mysql> create table t2 like t1;
Query OK,  rows affected (0.03 sec)
mysql> select * from t1;
+------+
| id   |
+------+
|     |
|     |
|     |
|     |
|     |
|     |
+------+
 rows in set (0.01 sec)
//复制表数据

mysql> insert into t2 select * from t1;
Query OK,  rows affected (0.00 sec)
Records:   Duplicates:   Warnings: 

mysql> select * from t2;
+------+
| id   |
+------+
|     |
|     |
|     |
|     |
|     |
|     |
+------+
 rows in set (0.00 sec)

添加索引

//添加主键索引
mysql> alter table t1 add primary key(id);
Query OK,  rows affected (0.01 sec)
Records:   Duplicates:   Warnings:
//添加唯一索引
mysql> alter table t1 add column name varchar() not null; //给t1表添加一个name列
Query OK,  rows affected (0.00 sec)
Records:   Duplicates:   Warnings:
//查看表信息
mysql> desc t1;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int()     | NO   | PRI |        |       |
| name  | varchar() | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
 rows in set (0.00 sec)
//清空表数据
mysql> truncate t1;
Query OK,  rows affected (0.00 sec)

mysql> select * from t1;
Empty set (0.00 sec)
//添加唯一索引
mysql> alter table t1 add unique index t1_name_unique(name);
Query OK,  rows affected (0.01 sec)
Records:   Duplicates:   Warnings:
//查看索引
mysql> show index from t1;
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name       | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| t1    |           | PRIMARY        |             | id          | A         |            |     NULL | NULL   |      | BTREE      |         |
| t1    |           | t1_name_unique |             | name        | A         |            |     NULL | NULL   |      | BTREE      |         |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
 rows in set (0.00 sec)
//添加普通索引
mysql> alter table t1 add column age int not null default ;
Query OK,  rows affected (0.01 sec)
Records:   Duplicates:   Warnings: 

mysql> desc t1
    -> ;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int()     | NO   | PRI |        |       |
| name  | varchar() | NO   | UNI | NULL    |       |
| age   | int()     | NO   |     |        |       |
+-------+-------------+------+-----+---------+-------+
 rows in set (0.00 sec)

mysql> alter table t1 add index t1_in_age(age);
Query OK,  rows affected (0.02 sec)
Records:   Duplicates:   Warnings: 

mysql> show index from t1;
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name       | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| t1    |           | PRIMARY        |             | id          | A         |            |     NULL | NULL   |      | BTREE      |         |
| t1    |           | t1_name_unique |             | name        | A         |            |     NULL | NULL   |      | BTREE      |         |
| t1    |           | t1_in_age      |             | age         | A         |        NULL |     NULL | NULL   |      | BTREE      |         |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
 rows in set (0.00 sec)

删除索引

mysql> alter table t1 drop primary key;

mysql> show index from t1;
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name       | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| t1    |           | t1_name_unique |             | name        | A         |            |     NULL | NULL   |      | BTREE      |         |
| t1    |           | t1_in_age      |             | age         | A         |        NULL |     NULL | NULL   |      | BTREE      |         |
+-------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
mysql> alter table t1 drop index t1_in_age;
Query OK,  rows affected (0.00 sec)
Records:   Duplicates:   Warnings: 

mysql> alter table t1 drop index t1_name_unique;
Query OK,  rows affected (0.01 sec)
Records:   Duplicates:   Warnings: 

mysql> show index from t1;
Empty set (0.00 sec)

设置字段自增长auto_increment

mysql> alter table t1 modify id int not null primary key auto_increment;
Query OK,  rows affected (0.02 sec)
Records:   Duplicates:   Warnings: 

mysql> desc t1;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int()     | NO   | PRI | NULL    | auto_increment |
| name  | varchar() | NO   |     | NULL    |                |
| age   | int()     | NO   |     |        |                |
+-------+-------------+------+-----+---------+----------------+
 rows in set (0.00 sec)

批量插入数据

mysql> insert into t1(name,age) values("aaa",),("bbb",),("cc",),("abc",);
Query OK,  rows affected (0.00 sec)
Records:   Duplicates:   Warnings: 

mysql> select * from t1;
+----+------+-----+
| id | name | age |
+----+------+-----+
|   | aaa  |   |
|   | bbb  |   |
|   | cc   |   |
|   | abc  |   |
+----+------+-----+
 rows in set (0.00 sec)

备份数据

mysql> select name,age from t1 into outfile "/tmp/t1.txt";
ERROR  (HY000): File '/tmp/t1.txt' already exists
mysql> select name,age from t1 into outfile "/tmp/t1.txt";
Query OK,  rows affected (0.00 sec)
[root@localhost tmp]# pwd
/tmp
[root@localhost tmp]# ls
ssh-TkEopz2496  ssh-zMKSLp2473  t1.txt  test.sql

清空表数据

mysql> delete from t1;
Query OK,  rows affected (0.00 sec)
mysql> select * from t1;
Empty set (0.00 sec)
//导入数据
mysql> load data infile '/tmp/t1.txt' into table t1(name,age);
Query OK,  rows affected,  warnings (0.00 sec)
Records:   Deleted:   Skipped:   Warnings:
//清空表
mysql> truncate t1;
Query OK,  rows affected (0.00 sec)
//两种清空表的方式在原理上不一样，我们可以看出delete方式的影响行数为32，而truncate则是0，那么也就是说delete是一行一行的删除的，
所以truncate在清楚数据上面比delete方式更高效，并且truncate会是auto_increment的值重置为1

重置auto_increment

mysql> delete from t1 where id > ;
Query OK,  rows affected (0.00 sec)

mysql> alter table t1 auto_increment=;
Query OK,  rows affected (0.01 sec)
Records:   Duplicates:   Warnings: 

load data方式导入数据，这种方式只是导入表数据而不会导入表结构，所以在单纯的数据导入上面更高效,我们可以看看导出文件的内容：

[root@localhost tmp]# cat t1.txt
aaa
bbb
cc
abc
aaa
bbb
cc
abc
aaa
bbb
cc
abc
aaa
bbb
cc
abc
aaa
bbb
cc
abc
aaa
bbb
cc
abc
aaa
bbb
cc
abc
aaa
bbb
cc
abc     

mysql> load data infile '/tmp/t1.txt' into table t1(name,age);
Query OK, 32 rows affected, 64 warnings (0.00 sec)
Records: 32  Deleted: 0  Skipped: 0  Warnings: 

case when语句

mysql> select id,name,age,case when age >=  then 'a' when age <= then 'b' else 'c' end as ddd from t1;
+----+------+-----+-----+
| id | name | age | ddd |
+----+------+-----+-----+
|   | aaa  |   | c   |
|   | bbb  |   | a   |
|   | cc   |   | b   |
|   | abc  |   | c   |
|   | aaa  |   | c   |
|   | bbb  |   | a   |
|   | cc   |   | b   |
|   | abc  |   | c   |
|   | aaa  |   | c   |
|  | bbb  |   | a   |
|  | cc   |   | b   |
|  | abc  |   | c   |
|  | aaa  |   | c   |
|  | bbb  |   | a   |
|  | cc   |   | b   |
|  | abc  |   | c   |
|  | aaa  |   | c   |
|  | bbb  |   | a   |
|  | cc   |   | b   |
|  | abc  |   | c   |
+----+------+-----+-----+
 rows in set (0.00 sec)

常用函数：字符串函数

//字符串组合函数
mysql> select concat("hello","mysql") as title;
+------------+
| title      |
+------------+
| hellomysql |
+------------+
 row in set (0.00 sec)

mysql> select concat("hello","mysql") as title;
+------------+
| title      |
+------------+
| hellomysql |
+------------+
 row in set (0.00 sec)

mysql> select concat("hello","mysql","aaaa") as title;
+----------------+
| title          |
+----------------+
| hellomysqlaaaa |
+----------------+
 row in set (0.00 sec)
//字符串大小写转换
mysql> select lcase('HELLO MYSQL') as title;
+-------------+
| title       |
+-------------+
| hello mysql |
+-------------+
 row in set (0.00 sec)

mysql> select ucase('hello mysql') as title;
+-------------+
| title       |
+-------------+
| HELLO MYSQL |
+-------------+
 row in set (0.00 sec)
//返回字符的长度
mysql> select length("hello mysql") as length;
+--------+
| length |
+--------+
|      |
+--------+
 row in set (0.00 sec)
//将字符重复N次
mysql> select repeat('hello mysql,',);
+--------------------------------------+
| repeat('hello mysql,',)             |
+--------------------------------------+
| hello mysql,hello mysql,hello mysql, |
+--------------------------------------+
 row in set (0.00 sec)
//替换字符串
mysql> select replace("hello mysql","mysql","php") as rp;
+-----------+
| rp        |
+-----------+
| hello php |
+-----------+
 row in set (0.00 sec)
//截取字符串，注意索引是从1开始
mysql> select substring("hello mysql",,) as sub;
+-------+
| sub   |
+-------+
| hello |
+-------+
 row in set (0.00 sec)
//返回字符在列表中的位置
mysql> select find_in_set("a","a,b,c,d");
+----------------------------+
| find_in_set("a","a,b,c,d") |
+----------------------------+
|                           |
+----------------------------+
 row in set (0.00 sec)

常用函数：数学函数

//10进制转2进制
mysql> select bin();
+--------+
| bin() |
+--------+
|      |
+--------+
 row in set (0.00 sec)
//向上取整
mysql> select ceiling(1.2);
+--------------+
| ceiling(1.2) |
+--------------+
|             |
+--------------+
 row in set (0.00 sec)
//向下取整
mysql> select floor(1.2);
+------------+
| floor(1.2) |
+------------+
|           |
+------------+
 row in set (0.00 sec)
//获取最大值
mysql> select *,max(age) from t1 ;
+----+------+-----+----------+
| id | name | age | max(age) |
+----+------+-----+----------+
|   | aaa  |   |        |
+----+------+-----+----------+
 row in set (0.00 sec)
//获取最小值
mysql> select *,min(age) from t1;
+----+------+-----+----------+
| id | name | age | min(age) |
+----+------+-----+----------+
|   | aaa  |   |        |
+----+------+-----+----------+
 row in set (0.00 sec)
//获取一个0到1之间的随机数
mysql> select rand();
+-------------------+
| rand()            |
+-------------------+
| 0.635864053513728 |
+-------------------+
 row in set (0.00 sec)

常用函数：日期函数

//获取当前时间的日期部分
mysql> select curdate();
+------------+
| curdate()  |
+------------+
| -- |
+------------+
 row in set (0.00 sec)
//获取当前时间的小时部分
mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| ::  |
+-----------+
 row in set (0.00 sec)
//获取当前时间
mysql> select now();
+---------------------+
| now()               |
+---------------------+
| -- :: |
+---------------------+
 row in set (0.00 sec)
//mysql> select unix_timestamp();
+------------------+
| unix_timestamp() |
+------------------+
|        |
+------------------+
 row in set (0.00 sec)
//获取当前时间戳
mysql> select unix_timestamp();
+------------------+
| unix_timestamp() |
+------------------+
|        |
+------------------+
 row in set (0.00 sec)
//时间戳转化为日期
mysql> select from_unixtime(unix_timestamp());
+---------------------------------+
| from_unixtime(unix_timestamp()) |
+---------------------------------+
| -- ::             |
+---------------------------------+
 row in set (0.00 sec)

//获取时间中的年月日
mysql> select year(now());
+-------------+
| year(now()) |
+-------------+
|         |
+-------------+
 row in set (0.00 sec)
mysql> select month(now());
+--------------+
| month(now()) |
+--------------+
|             |
+--------------+
 row in set (0.00 sec)
mysql> select day(now());
+------------+
| day(now()) |
+------------+
|          |
+------------+
 row in set (0.00 sec)