In SQL, procedures and functions are both database objects that allow you to encapsulate a sequence of SQL statements and execute them as a single unit. While they share some similarities, there are key differences between SQL procedures and SQL functions. Here’s an overview of their distinctions:
Procedure: Procedures do not return values. They are designed to perform an action or a series of actions without producing a result that can be used in an expression.
Function: Functions, on the other hand, must return a single value. This value can be of any data type, such as integer, string, or table.
Usage in Queries
Procedure: Procedures are invoked using the CALL or EXECUTE statement. They are typically used to perform an action or a set of actions, and they may have output parameters to return values.
Function: Functions can be used in queries much like any other expression. They are part of the SELECT statement and can be used to compute values that are then included in the result set.
Procedure: Procedures use the RETURN statement to exit and return a status code, but this does not return a value to the calling environment.
Function: Functions use the RETURN statement to return a value to the calling environment. This value is then used in expressions or assignments.
Procedure: Procedures can contain transaction control statements such as COMMIT and ROLLBACK, allowing for more fine-grained control over transactions.
Function: Functions are not allowed to contain transaction control statements. They are meant to be used in the context of a larger transaction controlled by the calling environment.
Procedure: Procedures can have exception handling using BEGIN…END blocks with handlers for specific conditions.
Function: Functions can handle exceptions, but they are more limited compared to procedures. They can use a basic BEGIN…END block for exception handling.
Use of Parameters
Procedure: Procedures can have input and output parameters. Output parameters can be used to return values to the calling environment.
Function: Functions can also have input parameters, and they always return a value. They can’t have output parameters like procedures.
In summary, while both procedures and functions in SQL allow you to encapsulate and execute a sequence of SQL statements, their key differences lie in their ability to return values, their usage in queries, and their support for transaction control and exception handling. Procedures are more focused on performing actions, while functions are designed to return a value for use in expressions.