MySQL data table operation DDL & data type

MySQL Basic operation - DDL

1、DDL explain

DDL（Data Definition Language） Data definition language

• Common operations on Database
• Common operations on table structure
• Modify table structure

Database -> Table

To the database 、 Table operations , No data involved

2、DDL Database operation

function	SQL
View all databases	show databases;
Create database	create database [if not exists] mydb1 [charset=utf8]
Switch 、 Select database	use mydb1;
Delete database	drop database [if exists] mydb1;
Modify database code	alter database mydb1 character set utf8;

3、DDL Data table operation

Create a table format

create table [if not exists] Table name (

​ Field name 1 type [( Width )] [ constraint condition ] [comment ‘ Field description ’],

​ Field name 2 type [( Width )] [ constraint condition ] [comment ‘ Field description ’]

)[ Some settings of the watch ];

Creating a table is to build an empty table , Specify the name of this table , This table has several columns , What is the name of each column , And the storage data type of each column .

use mydb1;

create table if not exists student (

​ sid int,

​ name varchar(20),

​ age int,

​ birth date,

​ address varchar(20)

);

data type

When defining field columns, you need to specify the data type and type size .

value type

integer , floating-point

type	size	Range ( A signed )	Range ( Unsigned )	purpose
TINYINT	1 byte	(-128,127)	(0,255)	Small integer value
SMALLINT	2byte	(-32768, 32767)	(0,65535)	Whole size The number
MEDIUMINT	3byte	(-8388608, 8388607)	(0, 16777215)	Large integer value
INT perhaps INTGER	4byte	(-2147483648, 2147483647)	(0, 4294967295)	Large integer value
BIGINT	8byte	(-9223372036854775808, 9223372036854775808)	(0, 18446744073709551615)	Maximal integer The number
DOUBLE	8byte	(-17976931348623157E+308, 17976931348623157E+308)	(0,22250738585072014E-308, 17976931348623157E+308)	Double precision floating point value
DECIMAL		Depend on M and D Value	Depend on M and D Value	Small value

String type

type	size	purpose
char	0-255bytes	Fixed length fixed character string
varchar	0-65536 bytes	Variable length delimiter string
tinyblog	0-255bytes	No more than 255 Binary string of characters
tinytext	0-255bytes	Text string
blog	0-65535 bytes	Long text data in binary form
text	0-65535 bytes	Long text data
mediumblog	0-16777215 bytes	Medium length text data in binary form
mediumtext	0-16777215 bytest	Medium length text data
longblog	0-4294967295 bytes	Maximum text data in binary form
longtext	0-4294967295 bytes	Large text data

Date and time type

type	size bytes	Range	Format	purpose
DATE	3 bytes	1000-01-01 9999-12-31	YYYY-MM-DD	Date value
TIME	3 bytes	-838:59:59 / 838:59:59	HH:MM:SS	Time value Or duration
YEAR	1 bytes	1901/2155	yyyy	The year is worth
DATETIME	8 bytes	1000-01-01 00:00:00 / 9999-12-31 23:59:59	YYYY-MM-DD HH:MM:SS	Mix date and time values
TIMESTAMP	4 bytes	1970-01-01 00:00:00 /2038 The end time is the 2147483647 second , Beijing time. 2038-1-19 11:14:07 , GMT 2038 year 1 month 19 Early morning 03:14:07	YYYYMMDD HH:MM:SS	Mix date and time values , Time stamp

4、 Common operations on table structure

function	SQL
View all table names of the current database	show tables;
View the creation statement of the specified table	show create table Table name ;
View table structure	desc Table name ;
Delete table	drop table Table name ;

Modify the table structure format

Modify the table to add columns

Grammar format ：

​ alter table Table name add Name type ( length ) [ constraint ]

Example ：

​ – by student Add a new field to the table as ： Is don't dept The type is varchar(20)

​ ALTER TABLE student ADD dept VARCHAR(20)

Change column name and type

Grammar format

​ alter table Table name change Old column names New column names type ( length ) [ constraint ];

Example ：

​ – by student Tabular dept Replace field with department varchar(30)

​ ALTER TABLE student change dept department VARCHAR(30);

Modify the order of fields in the table

alter table table_name modify  Property name   data type  first|after  Property name 2;
--  Example 1,  take isdel Move field to first place 
alter table table_name modify isdel tinyint(2) first; 

--  Example 2, take isdel Move field to id After column 
alter table table_name modify isdel tinyint(2) after id;

Modify table delete column

Grammar format ：

​ alter table Table name drop Name ;

Example ：

​ – Delete student Of table name department Column

​ ALTER TABLE student DROP department;

Modify the name of the table

Grammar format ：

​ rename table Table name to The new name of the table ;

Example ：

​ – Will table student Change its name to stu

​ RENAME TABLE student to stu;