Conditional Stored Procedure Creation in SQL Server

Stored procedures are precompiled collections of SQL statements, offering performance benefits and enhancing code reusability. However, deploying scripts that might include creating procedures that already exist can lead to errors. This tutorial explores techniques for conditionally creating or altering stored procedures in SQL Server, ensuring your scripts are robust and error-free.

The Problem: Errors When Creating Existing Procedures

When running a SQL script that attempts to create a stored procedure that already exists, SQL Server will raise an error. This is because the CREATE PROCEDURE statement expects a unique name. To avoid this, we need a way to check for the procedure’s existence before attempting to create it.

Methods for Checking Procedure Existence

Several approaches allow you to conditionally create or alter stored procedures. Here we’ll examine the most common and efficient techniques.

1. Using `OBJECT_ID`

The OBJECT_ID function is a powerful tool for determining if a database object exists. It returns the object ID of a specified database object. If the object doesn’t exist, it returns NULL.

Here’s how to use OBJECT_ID to conditionally create a stored procedure:

IF OBJECT_ID('dbo.MyProc') IS NULL
BEGIN
    -- Procedure does not exist, so create it
    CREATE PROCEDURE dbo.MyProc
    AS
    BEGIN
        -- Your stored procedure logic here
        SELECT 'Hello from MyProc!';
    END
END
ELSE
BEGIN
    -- Procedure already exists, optionally alter it or log a message
    -- You can use ALTER PROCEDURE to modify the existing procedure.
    -- Example:
    -- ALTER PROCEDURE dbo.MyProc AS SELECT 'Updated Hello from MyProc!';
    PRINT 'Procedure dbo.MyProc already exists.';
END

Explanation:

OBJECT_ID('dbo.MyProc'): This checks if a procedure named MyProc exists within the dbo schema. Remember to specify the schema.
IS NULL: If OBJECT_ID returns NULL, the procedure doesn’t exist.
CREATE PROCEDURE: If the procedure doesn’t exist, this statement creates it.
ALTER PROCEDURE: If the procedure does exist, you can use ALTER PROCEDURE to modify its definition.

Specifying Object Type with OBJECT_ID

For more precise checking, you can specify the object type as the second argument of OBJECT_ID. This is particularly important if you have objects with the same name but different types (e.g., a table and a stored procedure).

IF OBJECT_ID('dbo.MyProc', 'P') IS NULL
BEGIN
    -- Procedure does not exist, so create it
    CREATE PROCEDURE dbo.MyProc
    AS
    BEGIN
        -- Your stored procedure logic here
        SELECT 'Hello from MyProc!';
    END
END
ELSE
BEGIN
    -- Procedure already exists, optionally alter it or log a message
    PRINT 'Procedure dbo.MyProc already exists.';
END

Here, 'P' specifies that we are looking for a stored procedure. Other valid object types include 'U' for tables, 'V' for views, and so on.

2. Using `sys.objects` System View

Another approach is to query the sys.objects system view to check for the existence of the procedure.

IF NOT EXISTS (SELECT 1 FROM sys.objects WHERE type = 'P' AND name = 'MyProc')
BEGIN
    -- Procedure does not exist, so create it
    CREATE PROCEDURE dbo.MyProc
    AS
    BEGIN
        -- Your stored procedure logic here
        SELECT 'Hello from MyProc!';
    END
END
ELSE
BEGIN
    -- Procedure already exists, optionally alter it or log a message
    PRINT 'Procedure dbo.MyProc already exists.';
END

Explanation:

sys.objects: This system view contains metadata about all database objects.
WHERE type = 'P' AND name = 'MyProc': This filters the results to find objects of type ‘P’ (stored procedure) with the name ‘MyProc’.
NOT EXISTS: This checks if there are no matching objects, indicating that the procedure doesn’t exist.

3. `DROP PROCEDURE IF EXISTS` (SQL Server 2016 and Later)

SQL Server 2016 introduced the DROP PROCEDURE IF EXISTS statement, which simplifies the process considerably. This statement will only drop the procedure if it exists, avoiding errors.

DROP PROCEDURE IF EXISTS dbo.MyProc;

CREATE PROCEDURE dbo.MyProc
AS
BEGIN
    -- Your stored procedure logic here
    SELECT 'Hello from MyProc!';
END

This approach is the most concise and recommended solution for SQL Server 2016 and later versions. It effectively handles both creation and alteration scenarios.

Best Practices

Schema Qualification: Always specify the schema when referencing database objects (e.g., dbo.MyProc). This helps avoid ambiguity and potential errors.
Error Handling: Consider adding more robust error handling to your scripts to catch unexpected errors and provide informative messages.
Choose the Right Approach: Select the method that best suits your SQL Server version and coding style. DROP PROCEDURE IF EXISTS is the preferred choice for SQL Server 2016 and later.
Testing: Always test your scripts thoroughly in a development environment before deploying them to production.