MySQL introduction - crud Foundation (establishment of the prototype of the idea of adding, deleting, changing and searching)

CRUD

create,read,update,delete

1. Insert sentence （ Add data ）
2. Update sentence （ UPDATE statement ）
3. Delete sentence （ Delete data ）
4. Select sentence （ Find data ）

Insert sentence

Introductory cases

details

Update sentence

Introductory cases

details

1. UPDATE Syntax to update columns in the original table row with new values .
2. SET Clause to indicate which columns to modify and which values to give .
3. WHERE Clause specifies which rows should be updated . If not WHERE Clause , Then update all
   That's ok ( Record ), So the teacher reminds you to be careful .
   4. If you need to modify multiple fields , Can pass set Field 1 = value 1, Field 2- value …

update employee set salary = salary + 1000,job = ' Mountain patrolling ' where name = ' Old monster '

Delete sentence

Introductory cases

details

• If not used where Clause , All data in the table... Will be deleted .( Be careful )
• Delete Statement cannot delete a - The value of the column ( You can use update Set to null perhaps ’ ')
• Use delete Statement only delete records , Don't delete the table itself . To delete a table , Use droptable sentence .drop table Table name ;

drop table employee;

Select sentence 【 a key 】（ Single table , Multiple tables ）

matters needing attention

1. Select Specify which columns of data to query .
2. column Specifies the column name .
3. * Number means to query all columns .
4. From Specify which table to query .
5. DISTINCT Optional , When the result is displayed , Whether to remove duplicate data

Case practice

Create student table first

CREATE TABLE student (
	id INT NOT NULL DEFAULT 1,
	NAME VARCHAR ( 20 ) NOT NULL DEFAULT '',
	chinese FLOAT NOT NULL DEFAULT 0.0,
	english FLOAT NOT NULL DEFAULT 0.0,
	math FLOAT NOT NULL DEFAULT 0.0
	
);
INSERT INTO student
VALUES
	( 1, ' Taotao ', 98, 78, 90 );
INSERT INTO student
VALUES
	( 2, ' Zhang Fei ', 87, 50, 80 );
INSERT INTO student
VALUES
	( 3, ' Guan yu ', 91, 28, 30 );

Expression column

as sentence （ nickname ）

Case practice

where Clause common operators

Case practice 1

Case practice 2

Order by Clause

Basic introduction

1. Order by Specify sorted columns , The sorted column can be either the column name in the table , It can also be select The column name specified after the statement
2. Asc Ascending [ Default ]、Desc Descending
3. ORDER BY Clause should be in SELECT End of statement

Case presentation