Cuestionario de Bases de Datos

What type of trigger is executed before a DML operation occurs?

• AFTER

• BEFORE

• INSTEAD OF

• ON DELETE

Answer explanation

The correct choice is 'BEFORE' because it refers to triggers that execute prior to a DML operation, allowing for validation or modification of data before it is saved to the database.

Identify the error in this trigger: CREATE TRIGGER trg_example AFTER INSERT empleados BEGIN ... END;

Answer explanation

The error in the trigger definition is the missing 'FOR EACH ROW' clause. It should be 'CREATE TRIGGER trg_example AFTER INSERT ON empleados FOR EACH ROW BEGIN ... END;'. This clause specifies that the trigger will execute for each row affected.

Fill the blank: CREATE TRIGGER trg_update_salary (a)   UPDATE ON empleados FOR EACH ROW BEGIN ... END;

Answer explanation

La opción correcta es 'BEFORE' porque se utiliza para especificar que el trigger debe ejecutarse antes de que se realice la actualización en la tabla 'empleados'. Esto permite modificar datos antes de que se apliquen los cambios.

What is the keyword to define an input parameter in a procedure?

• IN

• OUT

• INOUT

• PARAM

Answer explanation

The keyword 'IN' is used to define an input parameter in a procedure, indicating that the parameter is for input only. 'OUT' and 'INOUT' serve different purposes, while 'PARAM' is not a valid keyword.

Short answer: What statement is used to delete a stored procedure called 'calcular_total'?

Answer explanation

To delete a stored procedure called 'calcular_total', you use the statement: DROP PROCEDURE calcular_total; This command removes the specified procedure from the database.

Fill in the blank: CREATE PROCEDURE ejemplo_proc( (a)   name VARCHAR(50) ) BEGIN ... END;

What statement is used to grant SELECT permissions on the 'clientes' table to the user 'juan'?

Answer explanation

To grant SELECT permissions on the 'clientes' table to the user 'juan', use the statement: GRANT SELECT ON clientes TO juan; This allows 'juan' to read data from the 'clientes' table.

Test type: Which of these statements correctly creates a user?

• CREATE USER 'juan'@'localhost' IDENTIFIED BY '1234';

• NEW USER juan IDENTIFIED BY '1234';

• CREATE ACCOUNT juan PASSWORD '1234';

• GRANT USER juan PASSWORD '1234';

Answer explanation

The correct statement to create a user in SQL is 'CREATE USER 'juan'@'localhost' IDENTIFIED BY '1234';'. The other options use incorrect syntax or commands that do not exist in SQL.

Find the error: GRANT SELECT clientes TO usuario1;

Answer explanation

The error is in the syntax. The correct command should be 'GRANT SELECT ON clientes TO usuario1;' to specify the table from which to grant permissions.

What is the main advantage offered by indexes?

• Reduce disk space

• Improve search performance

• Increase security

• Allow relationships between tables

Answer explanation

The main advantage of indexes is that they improve search performance by allowing the database to find and retrieve data more quickly, rather than scanning the entire table.