How do you use the SQL_VARIANT data type to store different data types in a single column?
NickCrt
Posted by NickCrt
Last Updated: August 03, 2024
SQL_VARIANT data_types
In SQL Server, the SQL_VARIANT data type allows you to store different data types in a single column. This feature is particularly useful when you want to store varying types of data without creating multiple columns for each type.
Steps to Use SQL_VARIANT:
1. Creation of Table with SQL_VARIANT Column: You define a column using the SQL_VARIANT data type when creating a table. Here is an example of how to create a table that includes a SQL_VARIANT column: 
CREATE TABLE ExampleTable (
       ID INT PRIMARY KEY,
       DataValue SQL_VARIANT
   );
2. Inserting Data: You can insert different data types into the SQL_VARIANT column. For instance: 
INSERT INTO ExampleTable (ID, DataValue)
   VALUES (1, 100),         -- Integer
          (2, 'Hello'),    -- String
          (3, GETDATE()),  -- DateTime
          (4, CAST(200.50 AS DECIMAL(10, 2))); -- Decimal
3. Retrieving Data: When retrieving data from a SQL_VARIANT column, you can use the SQL_VARIANT_PROPERTY function to determine the type of the stored value or cast the value to another data type: 
SELECT ID, 
          DataValue,
          SQL_VARIANT_PROPERTY(DataValue, 'BaseType') AS BaseType
   FROM ExampleTable;
This will give you the base type of the value stored in DataValue. 4. Casting Data: When using the values in operations, you'll likely need to cast them back to their original types. For example, if you know a particular row contains a string, you can cast it as follows: 
SELECT ID, 
          CAST(DataValue AS NVARCHAR(100)) AS StringValue
   FROM ExampleTable
   WHERE SQL_VARIANT_PROPERTY(DataValue, 'BaseType') = 'nvarchar';
Considerations:
- The SQL_VARIANT type can store data types such as int, float, decimal, char, nvarchar, datetime, and other scalar types, but it cannot store columns of types like TEXT, NTEXT, IMAGE, or USER-DEFINED TYPES. - The maximum storage size of a SQL_VARIANT is 8016 bytes, and the total length of the data stored will depend on the underlying data type. - Usage of SQL_VARIANT can complicate queries and performance; hence it's recommended to use it judiciously, especially in situations where the types of data to be stored are known and consistent. By following these steps and being aware of the considerations, you can effectively use the SQL_VARIANT data type in SQL Server to store multiple data types in a single column.
Default Image