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home / developersection / interviews / difference between function vs trigger?
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Ravi Vishwakarma
Ravi Vishwakarma

IT-Hardware & Networking

Ravi Vishwakarma is a dedicated Software Developer with a passion for crafting efficient and innovative solutions. With a keen eye for detail and years of experience, he excels in developing robust software systems that meet client needs. His expertise spans across multiple programming languages and technologies, making him a valuable asset in any software development project.

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1 Answers

Ravi Vishwakarma
Ravi Vishwakarma 12 May 2026
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In SQL, a FUNCTION and a TRIGGER are both database objects, but they serve very different purposes.

Main difference

FUNCTION TRIGGER
Called manually Runs automatically
Returns a value Usually does not return value
Used for computation/business logic Used for reacting to table events
Executed using SQL statements Executed when INSERT/UPDATE/DELETE occurs
Can be reused anywhere Attached to a table/event

1. SQL FUNCTION

A function is a reusable block of SQL logic that you explicitly call.

Example

CREATE FUNCTION add_numbers(a INT, b INT)
RETURNS INT
BEGIN
   RETURN a + b;
END;

Calling it:

SELECT add_numbers(5, 3);

Result:

8

Characteristics of functions

  • Accept parameters
  • Return a value
  • Called manually
  • Reusable
  • Used in queries

Common uses

  • Salary calculations
  • Formatting data
  • String operations
  • Business rules
  • Mathematical operations

2. SQL TRIGGER

A trigger automatically executes when an event happens on a table.

Events:

  • INSERT
  • UPDATE
  • DELETE

Example

CREATE TRIGGER user_created
AFTER INSERT ON users
FOR EACH ROW
BEGIN
   INSERT INTO logs(message)
   VALUES('New user added');
END;
  • Now whenever a row is inserted into users,
    the trigger runs automatically.
  • No manual call needed.

Characteristics of triggers

  • Event-driven
  • Automatic execution
  • Attached to a table
  • Executes before/after events
  • Used for automation

Trigger timing

BEFORE trigger

Runs before operation.

BEFORE INSERT

Use case:

  • Validation
  • Modifying values

AFTER trigger

Runs after operation.

AFTER UPDATE

Use case:

  • Logging
  • Notifications
  • Audit history

Visual comparison

FUNCTION flow

User/Query
    ↓
Calls function
    ↓
Function executes
    ↓
Returns value

TRIGGER flow

INSERT/UPDATE/DELETE happens
           ↓
Trigger fires automatically
           ↓
Trigger logic executes

Real-world examples

FUNCTION example

Calculate bonus:

SELECT calculate_bonus(50000);

TRIGGER example

Maintain audit log automatically:

Employee salary updated
        ↓
Trigger stores old salary in audit table

Important differences

Feature FUNCTION TRIGGER
Manual execution Yes No
Automatic execution No Yes
Attached to table No Yes
Returns value Yes Usually no
Can use in SELECT Yes No
Event-based No Yes

Example together

Suppose you have:

Function

CREATE FUNCTION tax(amount DECIMAL(10,2))
RETURNS DECIMAL(10,2)
BEGIN
   RETURN amount * 0.18;
END;

Used like:

SELECT tax(1000);

Trigger

CREATE TRIGGER save_history
AFTER UPDATE ON employees
FOR EACH ROW
BEGIN
   INSERT INTO employee_history(emp_id, old_salary)
   VALUES(OLD.id, OLD.salary);
END;

Automatically stores old salary whenever update happens.

Relationship between them

Sometimes triggers call functions internally.

Example:

UPDATE employees
       ↓
Trigger fires
       ↓
Trigger calls function
       ↓
Function calculates audit data

When to use FUNCTION

Use functions when:

  • You need reusable logic
  • Need returned values
  • Need calculations
  • Need query support

When to use TRIGGER

Use triggers when:

  • You need automatic actions
  • Need audit logs
  • Need history tracking
  • Need data validation
  • Need synchronization
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