feat: add the ability to create scalar indices (#679)

This is a pretty direct binding to the underlying lance capability

node/src/index.ts

@@ -24,7 +24,7 @@ import { isEmbeddingFunction } from './embedding/embedding_function'
 import { type Literal, toSQL } from './util'
 
 // eslint-disable-next-line @typescript-eslint/no-var-requires
-const { databaseNew, databaseTableNames, databaseOpenTable, databaseDropTable, tableCreate, tableAdd, tableCreateVectorIndex, tableCountRows, tableDelete, tableUpdate, tableCleanupOldVersions, tableCompactFiles, tableListIndices, tableIndexStats } = require('../native.js')
+const { databaseNew, databaseTableNames, databaseOpenTable, databaseDropTable, tableCreate, tableAdd, tableCreateScalarIndex, tableCreateVectorIndex, tableCountRows, tableDelete, tableUpdate, tableCleanupOldVersions, tableCompactFiles, tableListIndices, tableIndexStats } = require('../native.js')
 
 export { Query }
 export type { EmbeddingFunction }
@@ -223,6 +223,56 @@ export interface Table<T = number[]> {
    */
   createIndex: (indexParams: VectorIndexParams) => Promise<any>
 
+  /**
+   * Create a scalar index on this Table for the given column
+   *
+   * @param column The column to index
+   * @param replace If false, fail if an index already exists on the column
+   *
+   * Scalar indices, like vector indices, can be used to speed up scans.  A scalar
+   * index can speed up scans that contain filter expressions on the indexed column.
+   * For example, the following scan will be faster if the column `my_col` has
+   * a scalar index:
+   *
+   * ```ts
+   * const con = await lancedb.connect('./.lancedb');
+   * const table = await con.openTable('images');
+   * const results = await table.where('my_col = 7').execute();
+   * ```
+   *
+   * Scalar indices can also speed up scans containing a vector search and a
+   * prefilter:
+   *
+   * ```ts
+   * const con = await lancedb.connect('././lancedb');
+   * const table = await con.openTable('images');
+   * const results = await table.search([1.0, 2.0]).where('my_col != 7').prefilter(true);
+   * ```
+   *
+   * Scalar indices can only speed up scans for basic filters using
+   * equality, comparison, range (e.g. `my_col BETWEEN 0 AND 100`), and set
+   * membership (e.g. `my_col IN (0, 1, 2)`)
+   *
+   * Scalar indices can be used if the filter contains multiple indexed columns and
+   * the filter criteria are AND'd or OR'd together
+   * (e.g. `my_col < 0 AND other_col> 100`)
+   *
+   * Scalar indices may be used if the filter contains non-indexed columns but,
+   * depending on the structure of the filter, they may not be usable.  For example,
+   * if the column `not_indexed` does not have a scalar index then the filter
+   * `my_col = 0 OR not_indexed = 1` will not be able to use any scalar index on
+   * `my_col`.
+   *
+   * @examples
+   *
+   * ```ts
+   * const con = await lancedb.connect('././lancedb')
+   * const table = await con.openTable('images')
+   * await table.createScalarIndex('my_col')
+   * ```
+   */
+  createScalarIndex: (column: string, replace: boolean) => Promise<void>
+
   /**
    * Returns the number of rows in this table.
    */
@@ -537,6 +587,10 @@ export class LocalTable<T = number[]> implements Table<T> {
     return tableCreateVectorIndex.call(this._tbl, indexParams).then((newTable: any) => { this._tbl = newTable })
   }
 
+  async createScalarIndex (column: string, replace: boolean): Promise<void> {
+    return tableCreateScalarIndex.call(this._tbl, column, replace)
+  }
+
   /**
    * Returns the number of rows in this table.
    */

node/src/remote/index.ts

@@ -283,6 +283,10 @@ export class RemoteTable<T = number[]> implements Table<T> {
     }
   }
 
+  async createScalarIndex (column: string, replace: boolean): Promise<void> {
+    throw new Error('Not implemented')
+  }
+
   async countRows (): Promise<number> {
     const result = await this._client.post(`/v1/table/${this._name}/describe/`)
     return result.data?.stats?.num_rows

node/src/test/test.ts

@@ -135,6 +135,17 @@ describe('LanceDB client', function () {
       assert.isTrue(results.length === 10)
     })
 
+    it('should allow creation and use of scalar indices', async function () {
+      const uri = await createTestDB(16, 300)
+      const con = await lancedb.connect(uri)
+      const table = await con.openTable('vectors')
+      await table.createScalarIndex('id', true)
+
+      // Prefiltering should still work the same
+      const results = await table.search(new Array(16).fill(0.1)).limit(10).filter('id >= 10').prefilter(true).execute()
+      assert.isTrue(results.length === 10)
+    })
+
     it('select only a subset of columns', async function () {
       const uri = await createTestDB()
       const con = await lancedb.connect(uri)