Sql Server Alter Table

How to Change a Computed Column to a Regular Column in SQL Server

If you’re working with SQL Server, you may come across a situation where you need to change a computed column to a regular column. This might be necessary if you want to start storing data directly in the column instead of having it automatically calculated based on an expression. Unfortunately, SQL Server does not allow you to simply alter an existing computed column into a non-computed column while retaining its data. However, there’s a workaround that can achieve the desired outcome. In this blog post, we’ll walk through the process step by step.

Understanding Computed Columns

Before we dive into the solution, it’s essential to understand what a computed column is.

  • Computed Column: A computed column in SQL Server is a virtual column that is derived from an expression involving other columns in the same table. Its values are calculated automatically whenever a row is retrieved or modified.
  • Example: For instance, if you have a full_name column derived from first_name and last_name columns, SQL Server calculates full_name whenever you query the table.

Now, let’s explore the steps necessary to change a computed column into a regular column while preserving its current values.

Step-by-Step Solution

Step 1: Add a New Column to the Table

The first step is to create a new column in your existing table that will ultimately hold the values that were in the computed column. Here’s how you can do that:

ALTER TABLE YourTableName ADD NewColumnName DataType;

Replace YourTableName with the name of your table, NewColumnName with the name of the new column, and DataType with the desired data type (e.g., VARCHAR, INT, etc.) based on the expected values.

Step 2: Copy Data from the Computed Column

Next, you’ll want to transfer the data from the computed column to the new column you just created. You can do this using the UPDATE statement:

UPDATE YourTableName SET NewColumnName = ComputedColumnName;

Make sure to replace ComputedColumnName with the actual name of the computed column from which you’re copying the data.

Step 3: Drop the Computed Column

Now that you have the values stored in the new column, you can drop the old computed column. This will free up space in your table and complete the conversion:

ALTER TABLE YourTableName DROP COLUMN ComputedColumnName;

Step 4: Rename the New Column (Optional)

If you want the new column to have the same name as the old computed column for consistency, you can use:

EXEC sp_rename 'YourTableName.NewColumnName', 'ComputedColumnName', 'COLUMN';

Summary of the Process

To change a computed column into a non-computed column, follow these simple steps:

  1. Add a new column to the table.
  2. Copy the data from the computed column to the new column.
  3. Drop the computed column.
  4. (Optional) Rename the new column to retain the original name.

Conclusion

While SQL Server does not directly allow altering a computed column into a regular column, the steps outlined above provide a practical solution without losing your existing data. By adding a new column, copying the data, and then dropping the computed column, you can achieve your desired outcome effectively.

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