Microsoft Windows [Versión 10.0.19045.3570]
(c) Microsoft Corporation. Todos los derechos reservados.

C:\Windows\system32>mysql -u root -p
"mysql" no se reconoce como un comando interno o externo,
programa o archivo por lotes ejecutable.

C:\Windows\system32>cd c:/xampp/mysql/bin

c:\xampp\mysql\bin>mysql -u root -p
Enter password:
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 14
Server version: 10.4.28-MariaDB mariadb.org binary distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> create database trigger;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'trigger' at line 1
MariaDB [(none)]> create database trigger;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'trigger' at line 1
MariaDB [(none)]> create trigger;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1
MariaDB [(none)]> CREATE DATABASE alumnos;
Query OK, 1 row affected (0.001 sec)

MariaDB [(none)]> CREATE TABLE alumnos (
    ->     id INT AUTO_INCREMENT PRIMARY KEY,
    ->     nombre VARCHAR(50),
    ->     apellido VARCHAR(50),
    ->     edad INT,
    ->     direccion VARCHAR(100)
    -> );
ERROR 1046 (3D000): No database selected
MariaDB [(none)]> use alumnos;
Database changed
MariaDB [alumnos]> CREATE TABLE alumnos (
    ->     id INT AUTO_INCREMENT PRIMARY KEY,
    ->     nombre VARCHAR(50),
    ->     apellido VARCHAR(50),
    ->     edad INT,
    ->     direccion VARCHAR(100)
    -> );
Query OK, 0 rows affected (0.015 sec)

MariaDB [alumnos]> DELIMITER $$
MariaDB [alumnos]>
MariaDB [alumnos]> CREATE TRIGGER trigger_alumno_identificador
    -> BEFORE INSERT ON alumnos
    -> FOR EACH ROW
    -> BEGIN
    ->     SET NEW.identificador = CONCAT(NEW.id, '_', NEW.nombre, '_', NEW.apellido);
    -> END;
    -> $$
ERROR 1054 (42S22): Unknown column 'identificador' in 'NEW'
MariaDB [alumnos]>
MariaDB [alumnos]> ALTER TABLE alumnos ADD COLUMN identificador VARCHAR(255);
    -> ;
    -> ;
    -> ;;
    -> ;;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> ;
    -> Unknown column 'identificador' in 'NEW';
    -> ALTER TABLE alumnos ADD COLUMN identificador VARCHAR(255);
    -> DELIMITER $$
Query OK, 0 rows affected (0.008 sec)
Records: 0  Duplicates: 0  Warnings: 0

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ';
;
;;
;;
;
;
;
;
;
;
;
;
;
;
;
;
;
Unknown column 'identificador' in 'NEW';
...' at line 1
MariaDB [alumnos]>
MariaDB [alumnos]> CREATE TRIGGER trigger_alumno_identificador
    -> BEFORE INSERT ON alumnos
    -> FOR EACH ROW
    -> BEGIN
    ->     SET NEW.identificador = CONCAT(NEW.id, '_', NEW.nombre, '_', NEW.apellido);
    -> END;
    -> $$
Query OK, 0 rows affected (0.009 sec)

MariaDB [alumnos]>
MariaDB [alumnos]> DELIMITER ;
MariaDB [alumnos]> INSERT INTO alumnos (nombre, apellido, edad, direccion) VALUES ('Juan', 'Pérez', 20, 'Calle 123');
Query OK, 1 row affected (0.004 sec)

MariaDB [alumnos]> SELECT * FROM alumnos;
+----+--------+----------+------+-----------+---------------+
| id | nombre | apellido | edad | direccion | identificador |
+----+--------+----------+------+-----------+---------------+
|  1 | Juan   | Pérez    |   20 | Calle 123 | 0_Juan_Pérez  |
+----+--------+----------+------+-----------+---------------+
1 row in set (0.000 sec)

MariaDB [alumnos]> exit
Bye

c:\xampp\mysql\bin>mysqldump -u root -p --databases alumnos --events --routines --triggers > pruebatrigger.sql
Enter password:

c:\xampp\mysql\bin>