Difference Between Stored Procedure and Triggers in SQL

Stored Procedures

Stored Procedures is a group of pre-compiled SQL statements that is stored in a database and can be reused anytime. It allows you to do many things in one command. So doing several activities in a database will be easier and quicker than before. A stored procedure can be called from SQL commands as well as applications like Python, Java, or PHP.

Syntax

Following is the syntax to create a stored procedure ?

CREATE PROCEDURE procedure_name
AS
BEGIN
    -- SQL statements
END;

Example

Let us create a stored procedure where it fetches the data from Employees table. To create table named Employees use the following code -

CREATE TABLE Employees (
    Employee_id INT,
    Name VARCHAR(50),
    Salary DECIMAL(10, 2)
);

To insert records into Employees table we use INSERT command.

INSERT INTO Employees 
VALUES 
(1, 'Harry', 50000.00),
(2, 'Mohan', 60000.00);

Let's now construct a stored procedure that accesses every record in the Employees table.

DELIMITER #
CREATE PROCEDURE ListAllEmployees()
BEGIN
    SELECT * FROM Employees;
END #
DELIMITER ;

To call the procedure and view the output.

• Use EXEC or EXECUTE in SQL Server, Oracle, or PostgreSQL.
• Use CALL in MySQL.

To retrieve the list of all employees and their details, we will execute the stored procedure ListAllEmployees(). Following is the query -

CALL ListAllEmployees();

Following is the output of the above code ?

With the help of a stored procedure, We can save time because it reduces repetitive code and makes it simple to retrieve data through a single call.

Triggers

Triggers in SQL enable us to describe automatic operations that would be conducted as a result of specific actions happening within tables, such as INSERT, UPDATE, or DELETE. Triggers are very useful to automate repetitive database operations and maintain data integrity.

Syntax

Following is the syntax to create a trigger ?

DELIMITER #
CREATE TRIGGER trigger_name
AFTER | BEFORE [INSERT, UPDATE, DELETE]  ON table_name
FOR EACH ROW
BEGIN
    -- SQL statements
END #
DELIMITER;

Example

Let's create an AFTER INSERT trigger on the Employees table that logs each new insertion into the Log table. We have already created the Employees table in the above example. Let us now create a log table using the following code:

CREATE TABLE Log (
   log_id INT AUTO_INCREMENT PRIMARY KEY,
   employee_id INT,
   action VARCHAR(50)
);

This trigger automatically logs every insertion into the Employees table. When a new employee record is added, the trigger captures the employee_id and logs the action 'INSERT' into the Log table.

DELIMITER #
CREATE TRIGGER after_employee_insert
AFTER INSERT ON Employees
FOR EACH ROW
BEGIN
    INSERT INTO Log (employee_id, action)
    VALUES (NEW.employee_id, 'INSERT');
END #
DELIMITER ;

To activate the trigger we need to insert new records into the Employees table.

INSERT INTO Employees (Employee_id, Name, Salary)
VALUES 
(1, 'Alex', 33000.00);

After the insert, the log table will contain:

SELECT * FROM Log;

Following is the output of the above code ?

This shows that the trigger activated successfully when we added a unique record to the employee table.

Stored Procedure vs Triggers

The table below compares the key differences between stored procedures and triggers, highlighting their behavior, usage, and capabilities in database management.