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Author: alien
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Khóa học miễn phí MySQL – After Insert Trigger nhận dự án làm có lương
MySQL – After Insert Trigger
A Trigger is simply defined as a response to an event. In MySQL, a trigger is a special stored procedure that resides in the system catalogue, that is executed whenever an event is performed. These events include SQL statements like INSERT, UPDATE and DELETE etc.
It is called a special stored procedure as it does not require to be invoked explicitly like other stored procedures. The trigger acts automatically whenever the desired event is fired.
MySQL After Insert Trigger
The After Insert Trigger is a row-level trigger supported by the MySQL database. As its name suggests, the After Insert Trigger is executed right after a value is inserted into a database table.
A row-level trigger is a type of trigger that goes off every time a row is modified. Simply, for every single transaction made in a table (like insertion, deletion, update), one trigger acts automatically.
To elaborate, whenever an INSERT statement is executed in the database, the value is inserted into the table first followed by the trigger execution. Hence, one cannot update a newly inserted row using the AFTER INSERT trigger.
Syntax
Following is the syntax to create the AFTER INSERT trigger in MySQL −
CREATE TRIGGER trigger_name AFTER INSERT ON table_name FOR EACH ROW BEGIN -- trigger body END;
Example
Let us see an example demonstrating the AFTER INSERT trigger. In here, we are creating a new table named USERS, which contains the details of users of an application, using the following query −
CREATE TABLE USERS( ID INT AUTO_INCREMENT, NAME VARCHAR(100) NOT NULL, AGE INT NOT NULL, BIRTH_DATE VARCHAR(100), PRIMARY KEY(ID) );
Now, let us create another table ”PUSH_NOTIFICATIONS” that is used to store messages to send as push notifications to the users on their birthdays −
CREATE TABLE PUSH_NOTIFICATIONS( ID INT AUTO_INCREMENT, BIRTH_DATE VARCHAR(100), NOTIFICATIONS VARCHAR(255) NOT NULL, PRIMARY KEY(ID) );
Using the following CREATE TRIGGER statement, create a new trigger after_trigger on the USERS table to insert values into the PUSH_NOTIFICATIONS table −
DELIMITER // CREATE TRIGGER after_trigger AFTER INSERT ON USERS FOR EACH ROW BEGIN IF NEW.BIRTH_DATE IS NOT NULL THEN INSERT INTO PUSH_NOTIFICATIONS VALUES (new.ID, new.BIRTH_DATE, CONCAT(''Happy Birthday, '', NEW.NAME, ''!'')); END IF; END // DELIMITER ;Insert values into the USERS table using the regular INSERT statement as shown below −
INSERT INTO USERS (NAME, AGE, BIRTH_DATE) VALUES (''Sasha'', 23, ''24/06/1999''); (''Alex'', 21, ''12/01/2001'');Verification
To verify if the trigger has been executed, display the PUSH_NOTIFICATIONS table using the SELECT statement −
ID BIRTH_DATE NOTIFICATIONS 1 24/06/1999 Happy Birthday, Sasha! 2 12/01/2001 Happy Birthday, Alex!
Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc
Khóa học miễn phí MySQL – Drop Trigger nhận dự án làm có lương
MySQL – DROP TRIGGER
Triggers in MySQL are stored programs similar to procedures. These can be created on a table, schema, view and database that are associated with an event and whenever an event occurs the respective trigger is invoked.
Triggers are, in fact, written to be executed in response to any of the following events −
- A database manipulation (DML) statement (DELETE, INSERT, or UPDATE)
- A database definition (DDL) statement (CREATE, ALTER, or DROP).
- A database operation (SERVERERROR, LOGON, LOGOFF, STARTUP, or SHUTDOWN).
You can delete a trigger using the DROP TRIGGER Statement.
Dropping Trigger in MySQL
The DROP TRIGGER statement in MySQL will drop a trigger from a database, and all its information.
Syntax
Following is the syntax of the MySQL DELETE TRIGGER Statement.
DROP TRIGGER [IF EXISTS] trigger_name
Where, trigger_name is the name of the trigger you need to delete.
Example
Assume we have created a table with name student as shown below −
CREATE TABLE STUDENT( Name varchar(35), Age INT, Score INT );
Following query creates a trigger named sample_trigger on this table. This trigger will set the score value 0 if you enter a value that is less than 0 as score.
DELIMITER // CREATE TRIGGER sample_trigger BEFORE INSERT ON STUDENT FOR EACH ROW BEGIN IF NEW.score < 0 THEN SET NEW.score = 0; END IF; END // DELIMITER ;
Now, let us use the following query to drop the trigger we created in the previous step −
DROP TRIGGER sample_trigger;
Verification
To verify if the trigger has been dropped, let us display the trigger information using the following query −
SHOW TRIGGERSG
Since have deleted the trigger created, we get an empty set −
Empty set (0.11 sec)
With IF EXISTS clause
If you try to drop a trigger that doesn”t exist an error will be generated as shown below −
DROP TRIGGER demo;
Following is the output −
ERROR 1360 (HY000): Trigger does not exist
If you use the IF EXISTS clause along with the DROP TRIGEGR statement as shown below, the specified trigger will be dropped and if a trigger with the given name, doesn”t exist the query will be ignored.
DROP TRIGGER IF EXISTS demo;
Dropping Trigger Using a Client Program
In addition to create or show a trigger, we can also drop a trigger using a client program.
Syntax
To drop a trigger through a PHP program, we need to execute the DROP TRIGGER statement using the mysqli function query() as follows −
$sql = "Drop TRIGGER testTrigger"; $mysqli->query($sql);
To drop a trigger through a JavaScript program, we need to execute the DROP TRIGGER statement using the query() function of mysql2 library as follows −
sql = "DROP TRIGGER testTrigger"; con.query(sql);
To drop a trigger through a Java program, we need to execute the DROP TRIGGER statement using the JDBC function execute() as follows −
String sql = "DROP TRIGGER sample_trigger"; statement.execute(sql);
To drop a trigger through a python program, we need to execute the DROP TRIGGER statement using the execute() function of the MySQL Connector/Python as follows −
drop_trigger_query = "DROP TRIGGER sample_trigger" cursorObj.execute(drop_trigger_query)
Example
Following are the programs −
$dbhost = ''localhost
$dbuser = ''root
$dbpass = ''password
$db = ''TUTORIALS
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $db);
if($mysqli->connect_errno ) {
printf("Connect failed: %s
", $mysqli->connect_error);
exit();
}
//printf(''Connected successfully.
'');
$sql = "DROP TRIGGER testTrigger";
if($mysqli->query($sql)){
printf("Trigger dropped successfully...!");
}
if($mysqli->error){
printf("Failed..!" , $mysqli->error);
}
$mysqli->close();
Output
The output obtained is as follows −
Trigger dropped successfully...!
var mysql = require(''mysql2'');
var con = mysql.createConnection({
host:"localhost",
user:"root",
password:"password"
});
//Connecting to MySQL
con.connect(function(err) {
if (err) throw err;
//console.log("Connected successfully...!");
//console.log("--------------------------");
sql = "USE TUTORIALS";
con.query(sql);
sql = "DROP TRIGGER testTrigger";
con.query(sql);
console.log("Drop trigger query executed successfully..!");
console.log("Triggers: ");
sql = "SHOW TRIGGERS";
con.query(sql, function(err, result){
if (err) throw err;
console.log(result);
});
});
Output
The output produced is as follows −
Drop trigger query executed successfully..! Triggers: []
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class DropTrigger {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/TUTORIALS";
String user = "root";
String password = "password";
ResultSet rs;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection con = DriverManager.getConnection(url, user, password);
Statement st = con.createStatement();
//System.out.println("Database connected successfully...!");
String sql = "DROP TRIGGER sample_trigger";
st.execute(sql);
System.out.print("Triggerd dropped successfully...!");
}catch(Exception e) {
e.printStackTrace();
}
}
}
Output
The output obtained is as shown below −
Triggerd dropped successfully...!
import mysql.connector
# Establishing the connection
connection = mysql.connector.connect(
host=''localhost'',
user=''root'',
password=''password'',
database=''tut''
)
table_name = ''Student''
trigger_name = ''sample_trigger''
# Creating a cursor object
cursorObj = connection.cursor()
# drop trigger
drop_trigger_query = "DROP TRIGGER sample_trigger"
cursorObj.execute(drop_trigger_query)
print("Trigger is dropped successfully")
connection.commit()
# close the cursor and connection
cursorObj.close()
connection.close()
Output
Following is the output of the above code −
Trigger is dropped successfully
Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc