Stored Procedure vs Function in SQL: Key Differences
💡 Concept Name
Stored Procedure vs Function in SQL refers to two types of reusable blocks that encapsulate logic, but differ in return behavior, use cases, and how they're invoked.
📘 Quick Intro
A stored procedure performs tasks such as modifying data and supports multiple output methods, whereas a function is typically used for computations and must return a value. Functions can be used in SELECT statements; procedures cannot.
🧠 Analogy / Short Story
Imagine a stored procedure as a kitchen recipe that might cook, clean, and serve—you run it as a whole task. A function is like a juicer: it always takes input and returns a specific output (juice). You can plug a juicer into any kitchen (query), but you don’t use the whole recipe that way.
🔧 Technical Explanation
- ⚙️ A Stored Procedure can return multiple result sets or none; does not have to return a value.
- 📤 A Function must return a single value (scalar or table).
- 🔁 Procedures can call functions; functions can’t call procedures.
- 🧱 Functions can be used inside SELECT, WHERE, or JOIN clauses; procedures cannot.
- 💡 Functions are deterministic and side-effect-free; procedures can have side effects.
🎯 Purpose & Use Case
- ✅ Use stored procedures for multi-step data manipulation.
- ✅ Use functions for calculations, data validation, or returning values.
- ✅ Functions are ideal for reusable logic inside queries.
- ✅ Stored procedures are best for transactional workflows or batch processing.
💻 Real Code Example
-- Stored Procedure
CREATE PROCEDURE GetUsersByStatus
@Status NVARCHAR(10)
AS
BEGIN
SELECT * FROM Users WHERE Status = @Status;
END;
-- Function
CREATE FUNCTION GetUserFullName (@UserID INT)
RETURNS NVARCHAR(100)
AS
BEGIN
DECLARE @FullName NVARCHAR(100)
SELECT @FullName = FirstName + ' ' + LastName FROM Users WHERE ID = @UserID
RETURN @FullName
END;
-- Use Function in SELECT
SELECT dbo.GetUserFullName(1);
❓ Interview Q&A
Q1: Can a function return multiple result sets?
A: No. It can return only one value or table. Procedures can return multiple result sets.
Q2: Can you use a stored procedure inside a SELECT query?
A: No. Only functions can be used in queries.
Q3: Do functions support transactions?
A: No. Functions can’t begin transactions; procedures can.
Q4: When should you use a function over a procedure?
A: When you need a reusable computation that returns a value and can be embedded in a query.
Q5: Can functions modify database state?
A: No. They are expected to be side-effect-free; procedures can modify data.
📝 MCQs
Q1. Which of these always returns a value?
- Procedure
- Function
- Trigger
- Cursor
Q2. Where can a function be used that a procedure cannot?
- Transaction block
- DELETE command
- SELECT statement
- JOIN clause only
Q3. Can stored procedures return multiple results?
- Yes
- No
- Only in SQL Server
- Only in MySQL
Q4. Can a function modify data in the database?
- Yes
- No
- Only in Oracle
- Depends on return type
Q5. Which is more suitable for reusable logic in queries?
- Function
- Procedure
- View
- Trigger
💡 Bonus Insight
Use scalar functions for logic like formatting names or computing tax. Use inline table-valued functions to improve performance, as they behave more like views and allow query optimization.
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