SQL Server

The SQL Server Embedding Store integrates with the Vector search and vector indexes introduced in SQL Server 2025.

Maven Dependency

xml

<dependency>
    <groupId>dev.langchain4j</groupId>
    <artifactId>langchain4j-community-sqlserver</artifactId>
    <version>${latest version here}</version>
</dependency>

APIs

SQLServerEmbeddingStore

Usage

Instances of this store can be created by configuring a builder. The builder requires that a DataSource and an embedding table be provided.

It is recommended to configure a DataSource which pools connections, such as the Universal Connection Pool or Hikari. A connection pool will avoid the latency of repeatedly creating new database connections.

Examples of Embedding Store Configuration

If an embedding table already exists in your database, provide the table configuration:

java

EmbeddingStore<TextSegment> embeddingStore = SQLServerEmbeddingStore.dataSourceBuilder()
   .dataSource(myDataSource)
   .embeddingTable(EmbeddingTable.builder()
           .name("my_embedding_table")
           .dimension(384) // Must specify dimension
           .build())
   .build();

If the table does not already exist, it can be created by setting the create option:

java

EmbeddingStore<TextSegment> embeddingStore = SQLServerEmbeddingStore.dataSourceBuilder()
   .dataSource(myDataSource)
   .embeddingTable(EmbeddingTable.builder()
           .name("my_embedding_table")
           .createOption(CreateOption.CREATE)
           .dimension(384) 
           .build())
   .build();

The previous option will fail if the table already exists. In that case, you can use the CREATE_IF_NOT_EXISTS option:

java

EmbeddingStore<TextSegment> embeddingStore = SQLServerEmbeddingStore.dataSourceBuilder()
   .dataSource(myDataSource)
   .embeddingTable(EmbeddingTable.builder()
           .name("my_embedding_table")
           .createOption(CreateOption.CREATE_IF_NOT_EXISTS)
           .dimension(384) 
           .build())
   .build();

Finally, If you want to recreate the table, you can use the CREATE_OR_REPLACE option:

java

EmbeddingStore<TextSegment> embeddingStore = SQLServerEmbeddingStore.dataSourceBuilder()
   .dataSource(myDataSource)
   .embeddingTable(EmbeddingTable.builder()
           .name("my_embedding_table")
           .createOption(CreateOption.CREATE_OR_REPLACE)
           .dimension(384) 
           .build())
   .build();

If the columns of your existing table do not match the predefined column names or you would like to use different column names, you can customize the table configuration:

java

SQLServerEmbeddingStore embeddingStore =
SQLServerEmbeddingStore.dataSourceBuilder()
    .dataSource(myDataSource)
    .embeddingTable(EmbeddingTable.builder()
            .createOption(CreateOption.CREATE_OR_REPLACE)
            .name("my_embedding_table")
            .idColumn("id_column_name")
            .embeddingColumn("embedding_column_name")
            .textColumn("text_column_name")
            .metadataColumn("metadata_column_name")
            .dimension(1024)
            .build())
    .build();

You can also configure the SQL Server connection directly without providing a DataSource:

java

SQLServerEmbeddingStore embeddingStore =
SQLServerEmbeddingStore.connectionBuilder()
    .host("localhost")
    .port(1433)
    .database("MyDatabase")
    .userName("myuser")
    .password("mypassword")
    .embeddingTable(EmbeddingTable.builder()
            .name("embeddings")
            .createOption(CreateOption.CREATE_OR_REPLACE)
            .dimension(384)
            .build())
    .build();

Embeddings table schema

By default, the embedding table will have the following columns:

Name	Type	Description
id	NVARCHAR(36)	Primary key. Used to store UUID strings which are generated when the embedding store
embedding	VECTOR(dimension)	Stores the embedding using SQL Server 2025 native vector type
text	NVARCHAR(MAX)	Stores the text segment
metadata	JSON	Stores the metadata using SQL Server 2025 native JSON data type

Important Notes

Numeric Types

All number values are written as JSON Strings in the metadata fields to avoid overflow issues with numbers as Long.MAX_VALUE.

Vector Storage and Similarity

SQL Server 2025+ supports native VECTOR data types and this module uses the VECTOR_DISTANCE similarity function. This module supports the following metrics for the VECTOR_DISTANCE function:

COSINE: Cosine similarity (default)
EUCLIDEAN: Euclidean distance. The euclidean metric needs to perform some additional calculations to get the score from the distance.

JSON Metadata Support

SQL Server 2025 provides native JSON data type support and JSON indexing capabilities. The module uses the native JSON data type for metadata storage and supports creating JSON indexes for optimized metadata filtering using JSON_VALUE function.

You can configure JSON index creation for specific metadata keys, optionally indicating the order of the keys:

java

EmbeddingTable embeddingTable = EmbeddingTable.builder()
    .name("test_table")
    .createOption(CreateOption.CREATE_OR_REPLACE)
    .dimension(4)
    .build();

SQLServerEmbeddingStore embeddingStore =
    SQLServerEmbeddingStore.dataSourceBuilder()
        .dataSource(myDataSource)
        .embeddingTable(embeddingTable)
        .addIndex(Index.jsonIndexBuilder()
            .createOption(CreateOption.CREATE_OR_REPLACE)
            .key("author", String.class, JSONIndexBuilder.Order.ASC)
            .key("year", Integer.class)
            .build()
        )
        .build();

Indexes created with Index.jsonIndexBuilder() do not support the CreateOption.CREATE_IF_NOT_EXISTS option.

Limitations

Vector indexing performance depends on data size and distribution
DiskANN indexes on the vector column are not supported
The database collation should be set to a case-sensitive collation for metadata case-sensitive string comparisons
Distance DOT metric is not supported