MySQL learning notes -- addition, deletion, modification and query on a single table

notes ： Learning from this sister's blog https://blog.csdn.net/shine_a?type=blog

One ,sql and mysql The difference between

SQL Is a language developed for operating databases . It can operate the tables in the database , Such as modifying data , Find data .

For example, the following is SQL sentence .

-- increase 
INSERT  INTO  < Table name > （ Field name ）VALUES （ value ）;
-- Delete 
DELETE  FROM  < Table name >  WHERE  < filter >;
-- Change 
UPDATE  < Table name >  SET < Field name = value >  WHERE  < filter >;
-- check 
SELECT  < Field name >  FROM  < Table name >  WHERE  < filter >;

MySQL Is the computer software used to manage the database , This software also has Oracle、SQL Server etc. .

Two , install mysql

download MySQL：

https://dev.mysql.com/downloads/windows/installer/8.0.html

Open the URL above , The following interface will appear , Let's pick the first one Windows (x86, 32-bit), MSI Installer install .

install Mysql Will bring it mysql workbench Database graphical tools .

3、 ... and , Create database , And create a new table

--  Create database 
CREATE database Xiyouji;
--  Select database 
USE Xiyouji;
--  Create a people table  Roles：
CREATE TABLE Roles(
Sid INT ,
Sname VARCHAR(10),
Sex VARCHAR(10)
);
--  Insert statement 
INSERT INTO Roles VALUES
(1 , ' Pig eight quit '  , ' male '),
(2 , ' Tang Sanzang '  , ' male '),
(3 , ' The Monkey King '  , ' male '),
(4 , ' Sha Wujing '  , ' male '),
(5 , ' White dragon horse '  , ' male ');

Four , Use the command line to access the database

• SQL sentence Ignore case ,SELECT And select It's the same , For clarity of structure , all SQL Keywords are capitalized .
• SQL Statements ignore indents and line breaks , It's all made up of semicolons ; Division . Let's indent 、 Line breaks and so on are just to make the code look more beautiful , Structure is clearer .

 Connect to database ：mysql -u root -p
 Show existing databases ：show databases;
 Select database ：use [ Database name ]

5、 ... and ,select sentence

SELECT Statement is used to select data from the database , The results are stored in the result set .

SELECT < Field name > FROM < Table name >;

for example , We started with the “xiyouji” Look up the task table in the database “roles” All data for ,

1,select *

-- Select database 
USE xiyouji;
-- Select the table data to look up 
SELECT * FROM ROLES;

2,select Multiple fields

SELECT Sname,Sex FROM ROLES;

3,select Multiple fields

These fields may not be the existing column names in the table , It can also be Mathematical expression 、 Text . We use it AS Keyword to set column aliases （AS It can be omitted ）

SELECT Sname as ' full name ',Sex FROM ROLES;

4,SELECT Later fields , It can be used DISTINCT keyword , De duplication of data .

 SELECT DISTINCT Sname FROM ROLES;

6、 ... and ,where Clause

SELECT < Field name > FROM < Table name > WHERE < filter >;

1, Comparison operator

WHERE clause , The most commonly used is the comparison operator , Include greater than （>）、 Less than （<）、 be equal to （=）、 Greater than or equal to （>=）、 Less than or equal to （<=）、 It's not equal to （!= perhaps <>）. Note that it's an equal sign, not two equal signs .

SELECT * FROM ROLES WHERE Sname=' The Monkey King ';

2,AND,OR Operator

If AND and OR Use at the same time , it is to be noted that AND Priority over OR, But it's best to put parentheses , It's clearer .

 SELECT * FROM ROLES WHERE Sname=' The Monkey King 'OR Sname=' Sha Wujing ';

3,IN Operators and NOT IN Operator

 SELECT * FROM ROLES WHERE Sname IN (' Pig eight quit ',' The Monkey King ');

4,BETWEEN … AND Operator

BETWEEN … AND An interval consists of two end points .

SELECT * FROM ROLES WHERE Sid BETWEEN 2 AND 4;

5,LIKE Operators and NOT LIKE Operator

Fuzzy matching , Use this , Two wildcards are required .

%： Match any character 
_: Match a character 

SELECT * FROM ROLES WHERE SNAME LIKE '% enlightenment %';

6,REGEXP Regular expressions

Mainly used to search string , Than LIKE Operators are applicable to more scenarios .

^: start 
$: ending 
[abc]: contain abc
[a-c]: contain a-c
|: or 

-- Find names that contain “ ning ” Of the students 
WHERE Sname REGEXP ' ning ';
-- The search name is “ ning ” The first student 
WHERE Sname REGEXP '^ ning ';
-- The search name is “ ning ” The students at the end 
WHERE Sname REGEXP ' ning $';
-- The search name is “ ning ” or “ Twist “ The first student 
WHERE Sname REGEXP '^[ Ning Ning ]';
-- Find student number Sid yes 2 To 5（ Include 2 and 5） Of the students 
WHERE Sid REGEXP '[2-5]';
-- Find student number Sid yes 2 To 5 perhaps 7 To 9（ Include 2 and 5,7 and 9） Of the students 
WHERE Sid REGEXP '[2-5]|[7-9]';

Contains the word Wu and the word ma ：

 SELECT * FROM ROLES WHERE SNAME REGEXP '[ Wuma ]';

7,IS NULL Operators and IS NOT NULL Operator

 SELECT * FROM ROLES WHERE SNAME IS NULL;

7、 ... and ,ORDER BY Sort clause

SELECT < Field name > FROM < Table name > ORDER BY < Field name >;

You can sort not only numbers but also words , The field name after it can be the name of the column , The column name can be followed by a keyword .ASC It's in ascending order （ Default ）,DESC It's in descending order .

 SELECT * FROM ROLES WHERE SNAME REGEXP '[ Wuma ]' ORDER BY  SID DESC;

8、 ... and ,LIMIT Clause is used to limit the number of records returned

SELECT < Field name > FROM < Table name > LIMIT < Limit the number of rows >;

1、 Take the first few records

We can go through LIMIT n Take the first... In the result set n Bar record .

 SELECT * FROM ROLES LIMIT 3;

2, Skip the first few records

Can pass LIMIT m,n Skip the first... In the result set m Before records n Bar record .

When we want to skip 3 Data , Take... Directly 45 Two lines ：

 SELECT * FROM ROLES LIMIT 3,2;

Nine ,INSERT Insert statement

INSERT  INTO  < Table name > （ Name ）VALUES ( value );

1, You can do without specifying the column name , The inserted values must be completely inserted in the existing field order .

insert into roles values(9,' Princess Iron Fan ',' Woman ');

2, Column names can be specified , The order of the following values , If the order of the column names corresponds to .

insert into roles(Sid,Sname) values(10,' Zixia fairy ');

3、 Insert multiple rows , Multiple rows of data can be separated by commas between brackets .

 insert into roles values(11,' Which zha ',' male '),(12,' Erlang God ',' male '),(14,' Wheezing dog ',' male ');

Ten ,UPDATE UPDATE statement

UPDATE < Table name > SET < Field name = value > WHERE < filter >;

 update roles set Sex=' Woman ' where Sname=' Which zha ';

11、 ... and ,DELETE Delete statements

DELETE FROM < Table name > WHERE < filter >;

 DELETE FROM ROLES WHERE Sname=' Zixia fairy ';![ Please add a picture description ](https://img-blog.csdnimg.cn/f5a04ddf71fa4174a6d21ede9ba0ace7.png)