MySQL_ Addition, deletion and modification of data processing

The addition, deletion and modification of data processing can be learned in the following steps ：

• Use DML sentence

• insert data

• Update data

• Delete data

（1）DML（ Data manipulation language ）

• DML(Data Manipulation Language – Data manipulation language ) Can be performed under the following conditions ：
– Insert data into table
– Modify existing data
– Delete existing data
• A transaction is a process in which several tasks are performed DML The sentences make up

（2） insert data

INSERT Sentence syntax

• Use INSERT Statement inserts data into a table

INSERT INTO `user`(id,name,salary)
VALUES (9,' Xiao Luo ',7920);

• Using this syntax, you can only insert into a table at a time One data
• Character and date data should be enclosed in single quotes

INSERT INTO `user`(id,name,salary,hire_date)
VALUES (10,' Thank you ',5920,'2019-3-21');

Insert null values into the table

• Implicit mode ： Omit the value of the column in the column name table

INSERT INTO `user`(id,name)
VALUES (11,' Xiaofen ');

• Display mode :： stay VALUES Clause to specify a null value

INSERT INTO `user`
VALUES (12,' Trabecula ',NULL,NULL);

Inserts the specified value

NOW() function ： Record the date and time of the current system

INSERT INTO `user`(id,name,salary,hire_date)
VALUES (13,' Little thunder ',5600,NOW());

Copy data from other tables

• stay INSERT Add a subquery to the statement
• There's no need to write VALUES Clause
• The list of values in the subquery should be the same as INSERT The column name in Clause corresponds to

INSERT INTO `user`
SELECT *
FROM `student`
WHERE student_name LIKE ' Small %';

（3） Update data

UPDATE Sentence syntax

• Use UPDATE Statement update data
• You can update more than one piece of data at a time
• If you need to roll back data , It needs to be guaranteed in DML front , Set it up ： SET AUTOCOMMIT = FALSE
• Use WHERE Clause specifies the data to be updated

UPDATE `user`
SET id = 14
WHERE id = 18;

• If omitted WHERE Clause , Then all data in the table will be updated

UPDATE `user`
SET hire_date = '2021-8-24';

（4） Delete data

DELETE sentence

• Use DELETE Statement to delete data from a table
• Use WHERE Clause deletes the specified record

DELETE FROM `user`
WHERE id = 8;

• If omitted WHERE Clause , All data in the table will be deleted

DELETE FROM `student`;

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summary Through the above steps , You should learn how to use DML Statement to change data and transaction control

sentence	function
INSERT	Insert
UPDATE	to update
DELETE	Delete