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SQL Server vs Alopex DB
SQL Server 2025's vector type, vector indexes, and their limits. Also explains how it differs from Alopex DB.
Updated: Oct 12, 2026
What SQL Server is
SQL Server is Microsoft’s server-based relational database. SQL Server 2025, Azure SQL, and Fabric have a vector type.
How it works
- vector type: elements default to float32, up to 1,998 dimensions. With float16, up to 3,996 dimensions.
- Index: there is a vector index for approximate nearest neighbor search.
- Transfer: native binary transfer needs newer drivers (Microsoft.Data.SqlClient 6.1.0, JDBC 13.1.0 Preview, and others). Older clients get the varchar(max) representation.
Main features
T-SQL tables can hold vector columns and an index for approximate nearest neighbor search.
Limits
- In SQL Server 2025, float16 is in preview and requires PREVIEW_FEATURES to be enabled.
- A vector column cannot have constraints such as PRIMARY KEY, FOREIGN KEY, DEFAULT, or CHECK. It supports no comparison or arithmetic operators.
- A vector column cannot be in a memory-optimized table. Regular and columnstore indexes cannot be built on it.
- sp_describe_first_result_set does not return the vector type correctly, and many drivers see it as varchar or nvarchar.
- Ledger verification (sp_verify_database_ledger) fails if the database has a table with a vector column. Always Encrypted is not supported.
How it differs from Alopex DB
Both hold vectors in SQL tables and use an index for approximate nearest neighbor search.
Alopex DB has the vector type and HNSW index as core types and indexes. It embeds in your application as a single file.
Alopex DB embeds in the app and brings vector search and columnar tables. Try it locally; see the quickstart.