MySQL (II) - basic operation

Database operation

- Create database

CREATE DATABASE

# impact Name the database 
# if not exists Optional , prevent mysql Report errors 
CREATE DATABASE (if not exists) impact;

- List MySQL Database list

SHOW DATABASES

show databases;

- Using a database

USE Database name

use impact;
Database changed

- Determine the current database

SELECT DATABASE()

SELECT DATABASE();

- Delete database

DROP DATABASE Database name

# runoob Name the database ,IF EXISTS Optional , prevent mysql Report errors 
DROP DATABASE (IF EXISTS) runoob;

Database table operation

- All the tables in the database

SHOW TABLES

show tables;

- Create data table

CREATE TABLE Table name ()

#  The first column is the table field name , The second column is the data type 
#  Table field ',' separate 
# comment ' explain '  Optional , Properties of fields   Optional 
create table charact_tbl(
       id int comment ' Number ',
       name varchar(10) comment ' full name ',
       country varchar(10) comment ' Country ',
       sex varchar(1) comment ' Gender '
       ) comment ' Role table ';

- Query table structure

desc Table name

#  Multiple tables can be queried , Separated by commas 
desc charact_tb;

- Query the table creation statement of the specified table

SHOW CREATE TABLE Table name

show create table charact_tb;

- Modify the name of the table

ALTER TABLE Table name RENAME TO The new name of the table

ALTER TABLE charact_tb RENAME TO alter_tbl;

- Delete form

DROP TABLE (IF EXISTS) Table name

DROP TABLE IF EXISTS charact_tb;

- Delete the table and recreate （ format ）

TRUNCATE TABLE Table name

TRUNCATE TABLE charact_tbl;

- Add table fields

ALTER TABLE Table name ADD Field name type
Will be added to the end of the form

alter table charact_tb add age int;

- Modify field type and name

• ALTER TABLE Table name MODIFY Field name type ;
Only modify the data type

alter table charact_tb modify age tinyint;

• ALTER TABLE Table name MODIFY Field name new field name type

alter table charact_tb change age school varchar(10);

- Delete table fields

ALTER TABLE Table name DROP Table field name ;
If there is only one field left in the data table, it cannot be used DROP To delete fields

alter table charact_tb drop school;

- Query data from table

• SELECT Column name FROM The name of the table

#  Query multiple columns can be separated by commas 
select name from alter_tbl;

• SELECT * FROM The name of the table
'*' Represents all columns in the table

select * from alter_tbl;

- Insert data in the form

INSERT INTO Table name ( Table field )VALUES( Inserted data );

insert into user(name,age,school,grade,gender,date)
    ->  VALUES
    -> (" Xiao He ",17,"xx university "," Freshman "," Woman ",now());

where Clause

Used to specify the criteria for selection , It can be used to add, delete, query and modify

• Find data

SELECT Table field FROM The name of the table WHERE Table field Operator value

 select * from user where age>17;

AND and OR Operator

Further filtering of information

- AND Operator

#  Use AND Displays age greater than 17 And the grade is freshman 
 select * from user where age>17 AND grade=" Freshman ";

- OR Operator

#  Use OR Displays age greater than 17 Or the grade is freshman 
select * from user where age>17 OR grade=" Freshman ";

- Use at the same time OR and AND Operator

#  Use OR Displays age greater than 17 Or is a freshman and younger than 19
 select * from user where(age>17 OR grade=" Freshman ") AND age<19;

LIKE Clause

Fuzzy matching

- % wildcard

• After the character means that the matching starts from these characters

#  Inquire about id With 1 At the beginning 
select * from user where id LIKE "1%" ;

• Before the character generation, it means that the match ends with these characters

 #  Inquire about id With 1 At the end of the 
select * from user where id LIKE "%1" ;

• There are... On both sides of the character % Means to contain

#  The query date contains 16 Of 
select * from user where date LIKE "%16%" ;

- _ Operator

• Equivalent to replacing any 1 Characters

# _ Instead of the second place of age 
select * from user where age LIKE "1_" ;

IN The operator

stay WHERE Multiple values specified in clause

SELECT Table field FROM Table name WHERE Table field IN ( Table field value )

SELECT * FROM user WHERE age IN (16,17);

BETWEEN The operator

Select a data range between two values , and AND Continuous use

SELECT Table field FROM Table name WHERE Table field BETWEEN Table field value 1 AND Table field value 2

Include table field values 1, Include table field values 2

select * from user where id BETWEEN 1 AND 3;

stay BETWEEN Before to add NOT, Out of selection

select * from user where id NOT BETWEEN 4 AND 11;

UNION The operator

Merge two or more SELECT Result of statement

Duplicate values are not displayed

UNION ALL You can display duplicate values

Sort

ORDER BY Used to define how to sort

#  Default ascending order 
select * from employees order by last;

desc Descending

select * from employees order by last desc;

asc Ascending

 select * from employees order by last asc;

grouping

group by Group the data

#  Count count()
 select age ,count(*) from user group by age;

Update data

UPDATE Table name SET Field name = The new value WHERE Field name The operator value

update user SET school="xxx university " where age=16;

Delete data

DELETE FROM Table name WHERE Field name The operator value

delete from user where age<17;

JOIN Clause

- INNER JOIN

Get the records of field matching relationship in two tables
The two tables must match

select * from user inner join employees on employees.id=user.id;

This is equivalent to

select * from user ,employees where employees.id =user.id;

- LEFT JOIN

Get all the records in the left table , Even if the right table does not have a matching record

select * from employees left join user on employees.id=user.id order by employees.id ;

- RIGHT JOIN

Get all the records in the right table , Even if the left table does not have a matching record

select * from user right join employees on employees.id=user.id order by employees.id ;

SELECT DISTINCT sentence

List different values