How to Alter Column Datatype in SQL Server 2012
When working with SQL Server 2012, you may find yourself in a situation where you need to change the data type of a column in an existing table. This could be due to various reasons such as a change in the business requirements or to accommodate new data types. In this article, we will discuss the steps and best practices for altering column data types in SQL Server 2012.
Before you proceed with altering a column data type, it is essential to consider the following:
- Check if the column contains any data. If it does, ensure that the new data type can accommodate the existing data without any loss of information.
- Understand the implications of changing the data type. Changing a data type may affect the performance, storage requirements, and compatibility of your database.
- Make sure that you have the necessary permissions to alter the table structure.
Now, let’s dive into the steps to alter a column data type in SQL Server 2012:
Step 1: Identify the Table and Column
First, identify the table and the column you want to alter. You can use the following query to find the column data type:
“`sql
SELECT COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = ‘YourTableName’;
“`
Replace ‘YourTableName’ with the actual name of your table.
Step 2: Create a New Column with the Desired Data Type
Create a new column in the table with the desired data type. For example, if you want to change the ‘Age’ column from INT to VARCHAR(10), you can use the following SQL command:
“`sql
ALTER TABLE YourTableName
ADD AgeNew VARCHAR(10);
“`
Make sure to choose a suitable name for the new column, such as ‘AgeNew’ in this example.
Step 3: Update the Existing Data
Update the existing data in the new column to match the desired data type. This step is crucial to ensure that no data is lost during the data type change. Use the following SQL command to update the data:
“`sql
UPDATE YourTableName
SET AgeNew = CASE
WHEN Age IS NULL THEN NULL
WHEN CAST(Age AS VARCHAR(10)) = ” THEN ”
ELSE CAST(Age AS VARCHAR(10))
END;
“`
In this example, we are converting the ‘Age’ column data to VARCHAR(10). If the ‘Age’ column contains NULL values, we ensure that the ‘AgeNew’ column also contains NULL values. If the ‘Age’ column contains an empty string, we ensure that the ‘AgeNew’ column also contains an empty string. Otherwise, we convert the ‘Age’ column data to VARCHAR(10).
Step 4: Rename the New Column
Rename the new column to the original column name. Use the following SQL command to rename the column:
“`sql
EXEC sp_rename ‘YourTableName.AgeNew’, ‘Age’, ‘COLUMN’;
“`
Replace ‘YourTableName’ with the actual name of your table.
Step 5: Drop the Old Column
Finally, drop the old column from the table. Use the following SQL command to drop the column:
“`sql
ALTER TABLE YourTableName
DROP COLUMN Age;
“`
Replace ‘YourTableName’ with the actual name of your table.
By following these steps, you can successfully alter the data type of a column in SQL Server 2012. Always ensure that you have a backup of your database before making any structural changes to avoid data loss or corruption.
