1. Check all the databases
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1
|
show databases;
|
2. Create a database encoding format back
|
1
|
create database dbName charset=
'utf8'
;
|
3. Use / switch databases
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1
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use dbName
|
4. Check the database being used
|
1
|
select
database();
|
5. Delete Database
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1
|
drop database dbName;
|
MySQL data types
Integer type
| Integer type | Byte count | Sorry, the range of numbers | There are in line with the number of ranges |
| INTYINT | 1 | 0~255 | -128~127 |
| SMALLINT | 2 | 0~65535 | -32768~32767 |
| MEGIUMINT | 3 | 0~16777215 | -8388608~8388607 |
| INT | 4 | 0~4294967295 | -2147483648~2147483647 |
| INTEGER | 4 | 0~4294967295 | -2147483648~2147483647 |
| BIGINT | 8 | 0~18446744073709551615 | -9223372036854775808-9223372036854775807 |
Floating-point type
String type
When common type CHAR and VARCHAR strings, when below their differences
| Insert value | CHAR(5) | The number of bytes occupied | VARCHAR(5) | The number of bytes occupied |
| '' | '' | Five bytes | '' | A byte |
| '1' | '1' | Five bytes | '1' | Two bytes |
| '123' | '123' | Five bytes | '123' | Four bytes |
| '123 ' | '123 ' | Five bytes | '123 ' | Five bytes |
| '12345' | '12345' | Five bytes | '12345' | Six bytes |
TEXT is a special type of string type. TEXT can only save character data. As news content.
Types include TINYTEXT, TEXT, MEDIUMTEXT and LONGTEXT.
TEXT from the following 4 types of storage allows the length of the comparison
| Types of | Allowed length | storage |
| TINYTEXT | 0 to 255 bytes | Byte length of the value +2 |
| TEXT | 0 to 65535 bytes | Byte length of the value +2 |
| MEDIUMTEXT | 0 ~ 167,772,150 bytes | Byte length value +3 |
| LONGTEXT | 0 to 4,294,967,295 bytes | + 4 byte length of the value |
Date and Time Types
| Date Type | Byte count | Ranges | Zero value |
| YEAR | 1 | 1901~2155 | 0000 |
| DATE | 4 | 1000-01-01~9999-12-31 | 0000:00:00 |
| TIME | 3 | -838:59:59~838:59:59 | 00:00:00 |
| DATETIME | 8 | 1000-01-01 00:00:00~9999-12-31 23:59:59 | 0000-00-00 00:00:00 |
| TIMESTAMP | 4 | 19700101080001 | 00000000000000 |
表中常见的操作
1.查看当前数据库中的所有数据表
|
1
|
show tables;
|
2.创建表
create table tablename(字段1 数据类型,字段2 数据类型 ...) [charset set 字符集 collate 校对规则]
3.查看表结构
|
1
|
desc tablename;
|
4.重命名表
|
1
|
alter table 表原名 rename to 新表明;
|
5.添加字段
添加字段（默认添加在最后一个位置）
alter table tablename add 字段 数据类型;
添加字段：在表的第一个位置添加字段
alter table tablename add 字段数据类型 first;
添加字段: 在指定的位置添加字段
alter table tablename add 字段 new 数据类型 after 字段old;
6.修改字段
修改字段: 修改字段数据类型
alter table tablename modify 字段 数据类型;
修改字段: 修改字段到第一个位置
alter table tablename modify 字段数据类型 first;
修改字段：修改字段到指定位置
alter table tablename modify 字段数据类型 after 字段；
修改字段：只修改字段名称 不修改数据类型
alter table tablename change 字段 newname 原数据类型;
修改字段 修改字段名称 同时修改数据类型
alter table tablename change 字段 newname 新数据类型;
7.删除字段
alter table tablename drop 字段;
8.删除表
drop table tablename；