Common SQL statements (complete example)

This article is based on the school class 、 Student 、 Discipline 、 Performance and other scenes , practice SQL Use of statements

Create table

• Create class table

CREATE TABLE class(class_id INT auto_increment PRIMARY key,class_name VARCHAR(10));alter table class AUTO_INCREMENT =1;

• Create student table

CREATE TABLE student(stu_id INT AUTO_INCREMENT  PRIMARY KEY,stu_name VARCHAR(10),stu_sex VARCHAR(1),stu_age INT,class_id INT,foreign key(class_id) references class(class_id));alter table student AUTO_INCREMENT =1;

• Create chart of accounts

CREATE TABLE course(course_id INT auto_increment PRIMARY key,course_name VARCHAR(10));alter table course AUTO_INCREMENT =1;

• Create a score sheet

drop table score;CREATE TABLE score(id INT auto_increment PRIMARY key,stu_id INT,course_id INT,mark DECIMAL(3,1),foreign key(stu_id) references student(stu_id),foreign key(course_id) references course(course_id));alter table score AUTO_INCREMENT =1;desc score;

Insert data into the table

The operation table is class surface

insert into class values(NULL, ' 12 ')insert into class (`class_id`,`class_name`) values (NULL, ' One 3')insert into class (`class_name`) values (' One 4')

Use of stored procedures ： Bulk insert data

• Create stored procedure

CREATE PROCEDURE search_sex ( #search_user_name Is the name of the stored procedure     IN search_sex VARCHAR (20), # Incoming parameter     OUT count_number INT # Parameters returned ) READS SQL DATA # The program contains statements to read data BEGIN    SELECT        COUNT(*) INTO count_number    FROM        student    WHERE        stu_sex LIKE CONCAT('%', search_sex, '%');END

• Calling stored procedure

CALL search_sex(' Woman ', @nameCount);SELECT @nameCount;

• Use stored procedures to insert a large amount of data into the student table

# Create stored procedures to create large amounts of data drop PROCEDURE  if EXISTS insert_students;CREATE PROCEDURE insert_students(IN loop_times INT,IN stu_name CHAR,IN stu_sex CHAR,IN stu_age INT,IN class_id INT)BEGIN    DECLARE var INT DEFAULT 0;      WHILE var < loop_times DO        INSERT INTO student VALUES (NULL,concat(stu_name,CONVERT(var,CHAR)),stu_sex,stu_age,class_id);        SET var = var + 1;    END WHILE;ENDCALL insert_students(10,' money ',' male ',16,4);   

Look for statements

• Find all grades greater than 95 The name of the classmate

SELECT student.stu_name FROM score,studentwhere score.mark>95and student.stu_id=score.stu_idGROUP BY score.stu_idhaving count(*)>1

• The average query score is greater than 90 The list of students divided

SELECT score.stu_id,student.stu_name,AVG(score.mark)FROM score,student where student.stu_id=score.stu_idGROUP BY score.stu_id HAVING AVG(score.mark)>90

• Find out the students with the highest average score （ What if there are two at most ？？）

SELECT score.stu_id,student.stu_name,AVG(score.mark)FROM score,student where student.stu_id=score.stu_idGROUP BY score.stu_idORDER BY AVG(score.mark) desc LIMIT 1

author ： Test advanced

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