MySQL Procedures vs. Functions: When to Use Which?

Procedure vs Function in MySQL: Choosing the Right Tool

MySQL offers both procedures and functions as stored routines, but they differ in their purpose and usage.

Understanding the Key Difference

The primary distinction lies in the way they are invoked and used:

• Procedures: Invoked with a CALL statement, they perform operations without returning any value. They can modify tables, process records, and provide output parameters.
• Functions: Invoked within expressions, they return a single value directly to the caller and cannot pass back additional values.

Syntax and Structure

Procedure:

CREATE PROCEDURE proc_name ([parameters])
[characteristics]
routine_body

Function:

CREATE FUNCTION func_name ([parameters])
RETURNS data_type
[characteristics]
routine_body

• Functions require a RETURN value declaration, while procedures do not.
• Procedure parameters can be input, output, or both, while function parameters are only input.

Invocation and Execution

• Procedures are invoked using CALL statements.
• Functions are referenced within expressions or statements like other functions.

Additional Key Differences

• Procedures can generate result sets, while functions do not.
• Procedures can use dynamic SQL, while functions cannot.
• Functions are parsed at runtime, while procedures are precompiled.
• Functions do not impact the database state, while procedures can.
• Stored procedures can be recursive, while stored functions cannot.
• Stored functions cannot use FLUSH statements, while stored procedures can.

When to Use Which

• Functions: Use for calculations or retrieving data based on inputs.
• Procedures: Use for complex operations, changing database state, passing back multiple values, or generating result sets.

Consider the following scenario:

If you need to calculate the total cost of a customer order based on item prices and discounts, consider using a function.

If you want to insert customer information into a database, update inventory levels, and return the newly created customer ID, use a stored procedure.

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