Basic MySQL database operations

1、DDL Database operation of operation

--  View all databases 
show DATABASES;
--  Create database 
CREATE DATABASE [IF not EXISTS] mydb1 [CHARSET=UTF8];
--  Choose to use the database 
use mydb1;
--  Delete database 
drop DATABASE[ if EXISTS] mydb1;
--  Modify database code 
alter DATABASE mydb1 CHARACTER set utf8;

notes ：1. Things in brackets can be omitted , You need to remove the brackets before copying
2.IF not EXISTS（if EXISTS） The difference between adding and not adding is that there is no error when adding , If not, if the database exists （ non-existent ） May be an error .

2、DDL Operation table creation

--  choice mydb1
use mydb1;
--  Create table 
CREATE TABLE IF NOT EXISTS student(
sid int,
name varchar(20),
gender varchar(1),
age int,
birth date,
address varchar(20),
score double
);

data type ：
Data type refers to specifying the data type for the fields in the table when creating the table , Only data that meets the type requirements can be stored , The principle of using data types is ： Enough is enough. , Try to use a small range of , No big ones , To save storage space .

value type ：

type	size	Range （ A signed ）	Range （ Unsigned ）	purpose
TINYINT	1 byte	(-128,127)	(0,255)	Small integer value
SMALLINT	2 bytes	(-32768,32767)	(0,65535)	Large integer value
MEDIUMINT	3 bytes	(-8388608,8388607)	(0,16777215)	Large integer value
INT or INTEGER	4 bytes	(-2147483648,2147483647)	(0,4294967295)	Large integer value
BIGINT	8 bytes	(-9223372036854775808,9223372036854775087)	(0,18446744073709551615)	Maximum integer value
FLOAT	4 bytes	(-3.402823466E+38,3.402823466351E+38)	0,(1.175494351E-38,3.402823466E+38)	Single precision floating point values
DOUBLE	8 bytes	(-1.7976931348623157E+308,1.7976931348623157E+308)	0,(2.2250738585072014E-308,1.7976931348623157E+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	0-255 bytes	Fixed length string
VARCHAR	0-65535 bytes	Variable length string
TINYBLOB	0-255 bytes	No more than 255 Binary string of characters
TINYTEXT	0-255 bytes	Text string
BLOB	0-65535 bytes	Long text data in binary form
TEXT	0-65535 bytes	Long text data
MEDIUMBLOB	0-16777215 bytes	Medium length text data in binary form
MEDIUMTEXT	0-16777215 bytes	Medium length text data
LONGBLOB	0-4294967295 bytes	Maximum text data in binary form
LONGTEXT	0-4294967295 bytes	Large text data

The date type ：

type	size	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 byte	1907/2155	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 Japan In the morning 03:14:07	YYYYMMDD HHMMSS	Mix date and time values , Time stamp

3、DDL Table of operations other operations

 --  View all tables in the current database 
SHOW TABLES;
--  View the creation statement of the specified table 
SHOW CREATE TABLE student;
--  View table structure 
DESC student;
--  Delete table 
DROP TABLE student;

4、 Modify table structure

--  Add columns to ：alter table  Table name  add  listed   type （ length ）【 constraint 】;
ALTER TABLE student ADD dept VARCHAR(20);
--  Change column name and type :
-- alter table  Table name  change  Old column names   New column names   type （ length ） 【 constraint 】;
ALTER TABLE student CHANGE dept department VARCHAR(30);
--  Modify table delete column ：
-- alter table  Table name  drop  Name ;
ALTER TABLE student drop department;
--  Modify the name of the table ：
-- rename table  Table name  to  The new name of the table ;
RENAME TABLE student to stu;

• DML Data insertion for operation

--  Format 1：insert into  surface （ Name 1, Name 2……）values（ value 1, value 2……）;
--  Give one row of data at a time 
INSERT INTO stu(sid,name,gender,age,birth,address,score) 
VALUES(1001,' Zhang San ',' male ',18,'2001-12-23',' Beijing ',85.5);
--  Give multiple rows of data at a time 
INSERT INTO stu(sid,name,gender,age,birth,address,score) 
VALUES(1002,' Li Si ',' male ',18,'2001-10-23',' nanjing ',70.0),
(1003,' Wang Wu ',' Woman ',17,'2000-12-23',' Shenzhen ',88.5);
--  Assign values to only one or more values 
INSERT INTO stu(sid) values(1004);
INSERT INTO stu(sid,name) values(1005,' Zhao Liu ');

--  Format 2：insert into  surface values( value 1, value 2……);
INSERT INTO stu VALUES(1006,' Huang San ',' male ',18,'2001-5-23',' Beijing ',99.5);

notes ： Format 1 The case where multiple lines are given at one time in the format also applies 2

• DML Data modification of operation

--  Data modification 
--  Format 1：update  Table name  set  Field name  =  value , Field name = value ……;
--  Format 2：update  Table name  set  Field name = value , Field name = value ……where  Conditions ;
UPDATE stu set address = ' Chongqing ';
UPDATE stu set address = ' Beijing ' WHERE sid = 1004;
UPDATE stu set address = ' Shanghai ' WHERE sid >1004;

UPDATE stu set address = ' Beijing ',score = 100 WHERE sid = 1005;

• DML Data deletion of operation

--  Data deletion 
--  Format ：delete from  Table name  [where  Conditions ];
-- truncate table  Table name   perhaps  truncate  Table name 
DELETE FROM stu WHERE sid = 1004;
--  Delete all data in the table 
DELETE FROM stu;
--  Clear table data 
TRUNCATE TABLE stu;

notes ：delete and truncate The principle is different ,delete Only delete content , and truncate Be similar to drop table , It can be understood as deleting the whole table , Then create the table .

5、MySQL database DML Operation practice

MySQL database DML Operational exercises