When it comes to SQL, understanding the differences between stored procedures and functions is crucial. While they may seem similar at first glance, some key distinctions can impact their usefulness in different scenarios.

Firstly, a stored procedure can call a function, but a function cannot call a stored procedure. Additionally, a stored procedure can use temporary tables and table variables, whereas a function can only use table variables.

Handling exceptions is another area where these two structures differ. While a stored procedure can use a TRY...CATCH block to handle exceptions, a function cannot.

When it comes to joining tables, a function can be used in a JOIN clause, but a stored procedure cannot.

Stored procedures are also more versatile in terms of the values they can return. They can return zero, single, or multiple values (up to a maximum of 1024), whereas a function must always return a single result set, either scalar or a table.

Stored procedures can also perform data manipulation language (DML) operations, such as INSERT, UPDATE, and DELETE, while functions cannot. Functions are limited to being used in SELECT statements only.

While stored procedures can use explicit transactions, such as BEGIN TRAN, COMMIT, and ROLLBACK, functions cannot use transactions.

Another important distinction is that stored procedures are parsed, compiled, and stored in the database, while functions are compiled at run time.

Finally, while both structures can have input parameters, only stored procedures can have both input and output parameters.

In summary, while stored procedures and functions may seem similar, their differences can greatly impact their usefulness in different contexts. Understanding these differences is crucial for effectively using them in your SQL queries.