MySQL基础操作（一）
MySQL基础操作（一）:
1.1 mysql表复制
1.2 mysql索引
1.3 mysql视图
1.4 mysql内置函数
1.1 mysql表复制
复制表结构+复制表数据
create table t2 like t1;
insert into t2 select * from t1;
MariaDB [user]> create table t1(
-> id int unsigned auto_increment,
-> name varchar(30) not null,
-> primary key(id));
Query OK, 0 rows affected (0.00 sec)
MariaDB [user]> show tables;
+----------------+
| Tables_in_user |
+----------------+
| t1 |
+----------------+
1 row in set (0.00 sec)
MariaDB [user]> desc t1;
+-------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | NULL | |
+-------+------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
MariaDB [user]> insert into t2 select * from t1;
ERROR 1146 (42S02): Table 'user.t2' doesn't exist
MariaDB [user]> show tables;
+----------------+
| Tables_in_user |
+----------------+
| t1 |
+----------------+
1 row in set (0.00 sec)
MariaDB [user]> insert into t1(name) values('user1');
Query OK, 1 row affected (0.00 sec)
MariaDB [user]> insert into t1(name) values('user2');
Query OK, 1 row affected (0.00 sec)
MariaDB [user]> select * from t1;
+----+-------+
| id | name |
+----+-------+
| 1 | user1 |
| 2 | user2 |
+----+-------+
2 rows in set (0.00 sec)
MariaDB [user]> create table t2 like t1;
Query OK, 0 rows affected (0.00 sec)
MariaDB [user]> show tables;
+----------------+
| Tables_in_user |
+----------------+
| t1 |
| t2 |
+----------------+
2 rows in set (0.00 sec)
MariaDB [user]> desc t2;
+-------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | NULL | |
+-------+------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
MariaDB [user]> insert into t2 select * from t1;
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
MariaDB [user]> select * from t2;
+----+-------+
| id | name |
+----+-------+
| 1 | user1 |
| 2 | user2 |
+----+-------+
2 rows in set (0.00 sec)
1.2 mysql索引
1、alter table用来创建普通索引、unique索引或primary key索引
alter table table_name add index index_name(column_list)
alter table table_name add unique(column_list)
alter table table_name add primary key(column_list);
alter table table_name modify id int auto_increment;
2、create index
create table index index_name on table_name(column_list)create unique index index_name on table_name(column_list)
3、drop index
drop index index_name on table_name;4、alter table table drop
alter table table_name drop index index_name;
alter table t1 modify id int unsigned not null;
alter table table_name drop primary key;
1.3 mysql视图
1、创建视图：
mysql>create view v_t1 as select * from t1 where id>4 and id<8;2、view视图的帮助信息：
mysql>? viewalter view
create view
drop view
3、查看视图：
mysql>show tables;4、删除视图v_t1:
mysql>drop view v_t1;1.4 mysql内置函数
1、字符串函数：
concat(string[,...]) //连接字符串
lcase(string) //转换成小写
ucase(string) //转换成大写
length(string) //string长度
ltrim(string) //去除前端空格
rtrim(string) //去除后端空格
repeat(string,count) //重复count次
replace(str,search_str,replace_str) //在str中用replace_str替换search_str
substring(str,position,length) //从str的position开始，取length个字符
space(count) //生成count个空格
MariaDB [user]> select concat("hello","world") myname;
+------------+
| myname |
+------------+
| helloworld |
+------------+
1 row in set (0.00 sec)
MariaDB [user]> select lcase("MYSQL");
+----------------+
| lcase("MYSQL") |
+----------------+
| mysql |
+----------------+
1 row in set (0.00 sec)
MariaDB [user]> select ucase("mysql");
+----------------+
| ucase("mysql") |
+----------------+
| MYSQL |
+----------------+
1 row in set (0.00 sec)
MariaDB [user]> select length('linux');
+-----------------+
| length('linux') |
+-----------------+
| 5 |
+-----------------+
1 row in set (0.00 sec)
MariaDB [user]> select ltrim(" hello world");
+-------------------------------+
| ltrim(" hello world") |
+-------------------------------+
| hello world |
+-------------------------------+
1 row in set (0.00 sec)
MariaDB [user]> select rtrim("hello world ");
+---------------------------------+
| rtrim("hello world ") |
+---------------------------------+
| hello world |
+---------------------------------+
1 row in set (0.00 sec)
MariaDB [user]> select rtrim("hello world ! ");
+----------------------------------+
| rtrim("hello world ! ") |
+----------------------------------+
| hello world ! |
+----------------------------------+
1 row in set (0.00 sec)
MariaDB [user]> select repeat ('linux',3);
+--------------------+
| repeat ('linux',3) |
+--------------------+
| linuxlinuxlinux |
+--------------------+
1 row in set (0.00 sec)
MariaDB [user]> select replace('linux is very good','linux','php');
+---------------------------------------------+
| replace('linux is very good','linux','php') |
+---------------------------------------------+
| php is very good |
+---------------------------------------------+
1 row in set (0.00 sec)
MariaDB [user]> select substr('linux is very good',1,4) as linux;
+-------+
| linux |
+-------+
| linu |
+-------+
1 row in set (0.01 sec)
MariaDB [user]> select concat(space(20),'linux');
+---------------------------+
| concat(space(20),'linux') |
+---------------------------+
| linux |
+---------------------------+
1 row in set (0.00 sec)
2、数学函数：
bin(decimal_number) //十进制转二进制
chiling(number) //向上取整
floor(number) //向下取整
max(col) //取最大值,聚合时使用
min(col) //取最小值,聚合时使用
sqrt(num) //开平方
rand() //返回0-1内的随机数s
3、日期函数
curdate() //返回当前日期
curtime() //返回当前时间
now() //返回当前的日期时间
unix_timestamp(date) //返回当前date的unix时间戳
from_unixtime() //返回unix时间戳的日期指
week(date) //返回日期date为一年中的第几周
year(date) //返回日期date的年份
datediff(expr,expr2) //返回起始时间expr和结束时间expr2间天数