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Khóa học miễn phí MySQL – Drop Trigger nhận dự án làm có lương

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MySQL – DROP TRIGGER

Table of content

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

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