SQL Server 'Saving Changes Not Permitted' Error: Analysis and Solutions

Problem Description and Context

When working with table design in SQL Server Management Studio, users frequently encounter the error message: "Saving changes is not permitted. The change you have made requires the following table to be dropped and re-created. You have either made changes to a table that can't be recreated or enabled the option prevent saving changes that require the table to be re-created." This error typically occurs when attempting to modify table structure, even when the table is empty and unused.

Root Cause Analysis

SQL Server's designer requires table drop and recreation for specific types of structural modifications, stemming from SQL Server's internal handling of schema changes. The following operations trigger table recreation requirements:

• Adding a new column to the middle of the table
• Dropping an existing column
• Changing column nullability (NULL/NOT NULL)
• Changing the order of columns
• Changing the data type of a column

In the user's case of changing smallint to real, this data type modification falls under operations requiring table recreation. SQL Server employs this conservative approach to ensure data integrity and structural consistency, avoiding potential issues that could arise from direct modifications to complex table structures.

Solution and Configuration Adjustment

To resolve this issue, users can modify the SQL Server Management Studio designer options:

1. Open SQL Server Management Studio
2. Click the "Tools" menu and select "Options"
3. In the Options dialog, expand the "Designers" node
4. Select "Table and Database Designers"
5. Clear the "Prevent saving changes that require the table to be re-created" checkbox

After applying this configuration, the designer will permit changes that require table recreation. It's important to note that enabling this option means SQL Server will perform table drop and recreation processes in the background, which may impact performance for large tables or tables with complex constraints.

Technical Implementation Details

From a technical perspective, SQL Server handles table structure changes through two approaches: direct metadata modification and table recreation. For simple changes like adding nullable columns to the end of a table, the system can update metadata directly. However, for operations involving data reorganization or constraint changes, the system opts for the safer table recreation approach.

Here's a code example demonstrating how to safely execute data type changes through T-SQL statements:

-- Create temporary table for data storage
SELECT * INTO #TempTable FROM OriginalTable

-- Drop original table
DROP TABLE OriginalTable

-- Recreate table structure
CREATE TABLE OriginalTable (
    Column1 REAL,
    Column2 VARCHAR(50)
)

-- Restore data
INSERT INTO OriginalTable SELECT * FROM #TempTable

-- Clean up temporary table
DROP TABLE #TempTable

This method, while involving multiple steps, ensures data safety and operational reliability.

Best Practices and Recommendations

In practical development scenarios, development teams should configure designer options appropriately based on project requirements. For development environments, enabling table recreation functionality can improve development efficiency. For production environments, careful consideration should be given to the potential impacts of table recreation, with script-based structural changes recommended.

Additionally, before performing significant table structure modifications, always ensure proper data backups are in place and consider executing such operations during business off-peak hours to minimize system impact.