Should You Use SQL_Variant: Weighing Flexibility Against Performance and Limitations?

Understanding the Implications of Using SQL_Variant

In database design, the question of whether to use the SQL_Variant data type often arises. While it offers flexibility to store data of different types in a single column, its implications must be thoroughly considered.

Avoiding SQL_Variant: Reasons and Recommendations

According to industry experts, there are several reasons to avoid using SQL_Variant. These include:

• Limited Compatibility: SQL_Variant cannot be used in primary or foreign keys and computed columns.
• Inability for LIKE Queries: SQL_Variant does not support LIKE comparisons in WHERE clauses.
• Performance Overhead: OLE DB and ODBC providers automatically convert SQL_Variant to nvarchar(4000), potentially affecting performance.

Alternative Solutions

Given these limitations, alternative solutions are preferred:

• Separate Column Types: Use distinct columns for different data types, enabling optimal data interpretation and query efficiency.
• VARCHAR Column: Opt for a VARCHAR column if LIKE statements are essential.
• SQL_Variant (Last Resort): As a last resort, consider using SQL_Variant if other options are not feasible.

Exception:

However, it's important to note that starting with SQL Server 2005, SQL_Variant can be used in primary and foreign keys, subject to a maximum length of 900 bytes for the key values.

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