What are stored procedures in SQL?

Stored procedures in SQL are reusable blocks of code stored directly in a database. They encapsulate one or more SQL statements, allowing developers to execute complex operations with a single call. Think of them as functions for the database: you define the logic once, then reuse it across applications. Stored procedures are precompiled, which can improve performance, and they centralize business logic, making maintenance easier. For example, a stored procedure might handle inserting a new user into a database, validating inputs, and logging the action—all in one place.

A stored procedure typically includes parameters (inputs/outputs), SQL commands, and control structures like loops or conditionals. For instance, you could create a procedure called GetEmployeeDetails that accepts an employee ID and returns their name, department, and salary. Here’s a simplified example in SQL Server syntax:

CREATE PROCEDURE GetEmployeeDetails 
 @EmployeeID INT
AS
BEGIN
 SELECT Name, Department, Salary 
 FROM Employees 
 WHERE EmployeeID = @EmployeeID;
END;

This procedure can be called with EXEC GetEmployeeDetails 123, reducing repetitive code in applications. Stored procedures also support transactions, ensuring operations like transferring funds between accounts either fully succeed or roll back, maintaining data consistency.

The key benefits of stored procedures include performance gains (since they’re compiled once), enhanced security (by restricting direct table access and granting permission to run the procedure instead), and easier maintenance (logic is updated in one place). However, they can tie you to a specific database vendor due to syntax differences (e.g., T-SQL vs. PL/pgSQL). Overusing them might also push too much logic into the database, complicating debugging. Despite these trade-offs, stored procedures remain valuable for encapsulating complex, performance-critical operations close to the data layer.