MySQL common commands

One 、 Database operation

1. Create database

CREATE DATABASE  Database name ;

--  Create a name for python_test The database of 
CREATE DATABASE python_test; 

2. Delete database

DROP DATABASE  Database name ;

--  Delete name as python_test The database of 
DROP DATABASE python_test;  

3. View all databases

SHOW DATABASES;

4. Switch database

use  Database name ;

--  Select the name as python_test The database of 
use python_test;

5. sign out mysql

exit;

6. View the of creating the database SQL sentence

SHOW CREATE DATABASE  Database name ;

--  Show create database python_test Of SQL sentence 
SHOW CREATE DATABASE python_test; 

Two 、 Database table operation

1. Create table

CREATE TABLE students(id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT NOT NULL,NAME VARCHAR(20) NOT NULL,age TINYINT DEFAULT 0,gender ENUM(" male "," Woman ") DEFAULT " male ");

2. Delete table

DROP TABLE students; 

3. View the tables in the selected database

SHOW TABLES;

4. View table structure

DESC  Table name ;

5.ALTER operation

（1） Add a field to the table

ALTER TABLE  Table name  ADD  Field name   Field type ; 

--  to students Table add a birthday Field 
ALTER TABLE students ADD birthday DATETIME NOT NULL;  

（2） Modify the field type specified in the table

ALTER TABLE  Table name  MODIFY  Field name   Field type ;

--  modify students In the table birthday Type of field  
ALTER TABLE students MODIFY birthday DATE;  

（3） At the same time, modify the field name and field type of the table

ALTER TABLE  Table name  CHANGE  Original field name   new field name   New field type ;

--  modify students The original field in the table is birthday Field name and type 
ALTER TABLE students CHANGE birthday birth DATETIME NOT NULL; 

（4） Delete table specified fields

ALTER TABLE  Table name  DROP  Field name ;

--  Delete students In the table birth Field 
ALTER TABLE students DROP birth;  

6. Displays the... That created the specified table SQL sentence

SHOW CREATE TABLE  Table name ;

--  According to create students Tabular SQL sentence 
SHOW CREATE TABLE students; 

7.INSERT The insert

INSERT INTO  Table name  VALUES( Field 1 value , Field 2 value ,..., Field n value );

--  to students Table inserts a piece of data （ Insert one line ）
 --  The primary key column can be specified as  0,null,default
INSERT INTO students VALUES(0,'Tom',18,DEFAULT);
INSERT INTO students VALUES(DEFAULT,'Yellow',28,DEFAULT);
INSERT INTO students VALUES(NULL,'LiLei',38,DEFAULT);
 --  Some columns are inserted in a single row 
INSERT INTO students(NAME,age) VALUES('Bob',26);
 --  Insert all columns and rows 
INSERT INTO students VALUES(0,'Lisa',22,' Woman ');

--  to students The table inserts multiple pieces of data at one time （ Multi line insertion ）
 --  Partial column multi row insertion 
INSERT INTO students(NAME,age) VALUES('Jian',23),('Anla',40);
 --  Insert all columns and multiple rows 
INSERT INTO students VALUES(0,'Linda',25,' Woman '),(0,'Daive',27,' male ');

8.UPDATE update operation

UPDATE  Table name  SET  Field 1= value 1, Field 2= value 2,..., Field 2= value n WHERE  Field m= value m;	

--  modify students In the table NAME The field values for ‘Anla’ The data of 
UPDATE students SET age=33,gender=' Woman ' WHERE NAME='anla';

9.DELETE Delete operation

DELETE FROM students [WHERE  Field m= value m];

--  Delete all table data （ Physical delete ）
DELETE FROM  Table name ;

--  Delete the specified “ Field m= value m” The data of （ Physical delete ）
DELETE FROM  Table name  WHERE  Field m= value m;
 --  Physical delete students In the table "id=8" The data of 
DELETE FROM students WHERE id=8;

--  Set delete field is_del（ Logical deletion ）
UPDATE  Table name  SET is_del=1 WHERE  Field m= value m;
 --  Logical deletion students In the table NAME=‘Lisa’ The data of 
UPDATE students SET is_del=1 WHERE NAME='Lisa';

10.SELECT Query operation

Include ： Conditions of the query , Range queries , Fuzzy query , Empty judgment query , Sort , Paging query , Aggregate functions , Group query , Link query , Subquery

-- as and distinct The use of keywords in queries 
 -- as  names   Fields and tables can be used as Alias keywords 
SELECT  Field name 1 AS  Alias 1, Field name 2 AS  Alias 2,..., Field name n AS  Alias n FROM  Table name  AS  Table alias ;

 -- as  Alias query example 
SELECT NAME AS  full name ,age AS  Age  FROM students;
SELECT NAME AS  full name ,age AS  Age  FROM students AS s;
 --as  Keyword ellipsis form 
SELECT NAME  full name  FROM students s;


 -- distinct  duplicate removal   Remove the data in the same field name in the query , Keep only one piece of data 
SELECT DISTINCT  Field name 1[, Field name 2,..., Field name n] from  Table name ;

 -- distinct Example of de duplication query 
SELECT DISTINCT gender FROM students;
SELECT DISTINCT age,gender FROM students;

--------------------------------------------------
--  Conditions of the query ：where
 --  Comparison operator ： > , >= , < , <= , !=
SELECT * FROM students WHERE id>3;  --  Inquire about id>3 Student information 
SELECT * FROM students WHERE id<=4;   
SELECT * FROM students WHERE NAME!='Bob'; --  Inquire about name No Bob Information about 
 
 -- Logical operators ：and , or , not
SELECT * FROM students WHERE id>3 AND gender=' Woman ';	--  Inquire about id Range greater than 3 And the gender is ‘ Woman ’ Information about 
SELECT * FROM students WHERE id<4 OR is_del=0;   --  Interlude id Range is less than 4 Or delete the tag 0 Information about 
SELECT * FROM students WHERE NOT (age>=18 AND age<=30);

--------------------------------------------------
--  Range queries ：between ... and , in
SELECT * FROM students WHERE id BETWEEN 3 AND 8;   --  Inquire about id The scope is 3-8 Information about 
SELECT * FROM students WHERE NOT (id BETWEEN 3 AND 8); 
SELECT * FROM students WHERE id IN (1,3,5,7);   --  Inquire about id The scope is （1,3,5,7） Information about 
SELECT * FROM students WHERE id NOT IN (1,3,5,7);

--------------------------------------------------
--  Fuzzy query ：like [  With regular expressions  "%"( Any number of keywords ) , "_"( Any keyword ) ]
SELECT * FROM students WHERE NAME LIKE 'L%';
SELECT * FROM students WHERE NAME LIKE 'L___';
SELECT * FROM students WHERE NAME LIKE '%w' OR NAME LIKE 'L%';

--------------------------------------------------
--  Empty judgment query ：is null , is not null
SELECT * FROM students WHERE height IS NULL;  --  Search for information with height empty 
SELECT * FROM students WHERE height IS NOT NULL; --  Query the information that the height is not empty 

--------------------------------------------------
--  Sort ：order by  Ascending (order by  Field name  ASC)  Descending (order by  Field name  DESC)
SELECT * FROM students WHERE gender=' male ' AND is_del=0 ORDER BY id DESC;   --  Query the information that the gender is male and has not been deleted , Descending order 
SELECT * FROM students ORDER BY age DESC;
SELECT * FROM students ORDER BY age DESC,height DESC;   --  First, in descending order of age , If the age is the same, they will be arranged in descending order of height 
SELECT * FROM students ORDER BY age ASC;

--------------------------------------------------
--  Paging query 
select * from  Table name  limit start,count;  -- start Is the start row index ,count Is the number of queries 
SELECT * FROM students WHERE gender=' male ' LIMIT 0,3;  --  The first three data show that gender is male 
SELECT * FROM students WHERE gender=' male ' LIMIT 3;  --  Abbreviation ：  The first three data show that gender is male 

--  For the first n Page data 
SELECT * FROM students LIMIT (n-1)*m,m;

--------------------------------------------------
--  Aggregate functions （ Generally, statistics are carried out in combination with grouping   incorrect null Make statistics ）
 -- count(col)  Indicates the total row number of the specified column 
SELECT COUNT(id) FROM students;
SELECT COUNT(*) FROM students;

 -- max(col)  Indicates the maximum value of the specified column 
SELECT MAX(id) FROM students WHERE gender=' Woman ';

 -- min(col)  Means to find the minimum value of the specified column 
SELECT MIN(id) FROM students WHERE is_del=0;

 -- sum(col)  Indicates the sum of the specified columns 
SELECT SUM(height) FROM students WHERE gender=' male ';

 -- avg(col)  Indicates that the average value of the specified column 
SELECT AVG(height) FROM students WHERE gender=' male ';
SELECT AVG(IFNULL(height,0)) FROM students WHERE gender=' male ';  --  Null value found as 0 Make statistics 

--------------------------------------------------
--  Group query 
 --group by  Field name  ( After grouping according to the specified field, you can only query according to the specified field )
SELECT gender FROM students GROUP BY gender;   
SELECT gender,name FROM students GROUP BY gender,name; 

 -- group_concat( Field name ) ( Count the information set of the specified field name according to the specified grouping field name )
   --  according to gender Grouping （ It's actually divided into   male   Woman   Two sets ）, And statistics name The distribution of fields in male and female sets , Use ',' Segmentation 
SELECT gender,GROUP_CONCAT(NAME) FROM students GROUP BY gender;
SELECT gender,AVG(age) FROM students GROUP BY gender;
SELECT gender,COUNT(*) FROM students GROUP BY gender;

 --  Use having
SELECT gender,COUNT(*) FROM students GROUP BY gender HAVING COUNT(*)>3;

 -- with rollup  Add summary information to the last line   Only the column of set function will be summarized 
SELECT gender,COUNT(*) FROM students GROUP BY gender WITH ROLLUP;
SELECT gender,GROUP_CONCAT(age) FROM students GROUP BY gender WITH ROLLUP;

--------------------------------------------------
--  Link query  ( Realize the joint table query of multiple tables )
 --  Internal connection   Public data that meets the conditions of multiple tables   intersection 
select  Field  from  surface 1 inner join  surface 2 on  surface 1. Field = surface 2. Field 
SELECT * FROM students INNER JOIN class ON students.c_id=class.id;
SELECT s.name,c.name FROM students AS s INNER JOIN class AS c ON s.c_id=c.id;

 --  Left connection   Query the data in the right table based on the left table , If the data in the right table does not exist according to the query criteria, use null fill  left On the left is the left watch , On the right is the right watch 
select  Field  from  surface 1 left join  surface 2 on  surface 1. Field 1= surface 2. Field 2;
SELECT * FROM students LEFT JOIN class ON students.c_id=class.id;
SELECT * FROM students AS s LEFT JOIN class AS c ON s.c_id=c.id;

 --  Right link   Query the data of the left table based on the right table , If the data in the left table does not exist according to the query criteria, use NULL fill  right On the left is the left watch , On the right is the right watch 
select  Field  from  surface 1 right join  surface 2 on  surface 1. Field 1= surface 2. Field 2
SELECT * FROM students AS s RIGHT JOIN class AS c ON s.c_id=c.id;

 --  Self join   The left table and the right table are the same table   Is to connect a table inside 
CREATE TABLE areas(id VARCHAR(20) PRIMARY KEY NOT NULL,title VARCHAR(20) NOT NULL,pid VARCHAR(20));


--  Subquery  ( stay select Nested in a statement select sentence )
SELECT * FROM students WHERE age>(SELECT AVG(IFNULL(age,0)) FROM students);