@lancedb/lancedb • Docs

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@lancedb/lancedb / QueryBase

Class: QueryBase<NativeQueryType>

Common methods supported by all query types

Extended by

• Query
• VectorQuery

Type Parameters

• NativeQueryType extends NativeQuery | NativeVectorQuery

Implements

• AsyncIterable<RecordBatch>

Constructors

new QueryBase()

protected new QueryBase<NativeQueryType>(inner): QueryBase<NativeQueryType>

Parameters

• inner: NativeQueryType | Promise<NativeQueryType>

Returns

QueryBase<NativeQueryType>

Properties

inner

protected inner: NativeQueryType | Promise<NativeQueryType>

Methods

[asyncIterator]()

[asyncIterator](): AsyncIterator<RecordBatch<any>, any, undefined>

Returns

AsyncIterator<RecordBatch<any>, any, undefined>

Implementation of

AsyncIterable.[asyncIterator]

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doCall()

protected doCall(fn): void

Parameters

• fn

Returns

void

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execute()

protected execute(options?): RecordBatchIterator

Execute the query and return the results as an

Parameters

• options?: Partial<QueryExecutionOptions>

Returns

RecordBatchIterator

See

• AsyncIterator of
• RecordBatch.

By default, LanceDb will use many threads to calculate results and, when the result set is large, multiple batches will be processed at one time. This readahead is limited however and backpressure will be applied if this stream is consumed slowly (this constrains the maximum memory used by a single query)

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explainPlan()

explainPlan(verbose): Promise<string>

Generates an explanation of the query execution plan.

Parameters

• verbose: boolean = false

If true, provides a more detailed explanation. Defaults to false.

Returns

Promise<string>

A Promise that resolves to a string containing the query execution plan explanation.

Example

import * as lancedb from "@lancedb/lancedb"
const db = await lancedb.connect("./.lancedb");
const table = await db.createTable("my_table", [
  { vector: [1.1, 0.9], id: "1" },
]);
const plan = await table.query().nearestTo([0.5, 0.2]).explainPlan();

---

filter()

filter(predicate): this

A filter statement to be applied to this query.

Parameters

• predicate: string

Returns

this

Alias

where

Deprecated

Use where instead

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limit()

limit(limit): this

Set the maximum number of results to return.

By default, a plain search has no limit. If this method is not called then every valid row from the table will be returned.

Parameters

• limit: number

Returns

this

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nativeExecute()

protected nativeExecute(options?): Promise<RecordBatchIterator>

Parameters

• options?: Partial<QueryExecutionOptions>

Returns

Promise<RecordBatchIterator>

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select()

select(columns): this

Return only the specified columns.

By default a query will return all columns from the table. However, this can have a very significant impact on latency. LanceDb stores data in a columnar fashion. This means we can finely tune our I/O to select exactly the columns we need.

As a best practice you should always limit queries to the columns that you need. If you pass in an array of column names then only those columns will be returned.

You can also use this method to create new "dynamic" columns based on your existing columns. For example, you may not care about "a" or "b" but instead simply want "a + b". This is often seen in the SELECT clause of an SQL query (e.g. SELECT a+b FROM my_table).

To create dynamic columns you can pass in a Map. A column will be returned for each entry in the map. The key provides the name of the column. The value is an SQL string used to specify how the column is calculated.

For example, an SQL query might state SELECT a + b AS combined, c. The equivalent input to this method would be:

Parameters

• columns: string | string[] | Record<string, string> | Map<string, string>

Returns

this

Example

new Map([["combined", "a + b"], ["c", "c"]])

Columns will always be returned in the order given, even if that order is different than
the order used when adding the data.

Note that you can pass in a `Record<string, string>` (e.g. an object literal). This method
uses `Object.entries` which should preserve the insertion order of the object.  However,
object insertion order is easy to get wrong and `Map` is more foolproof.

---

toArray()

toArray(options?): Promise<any[]>

Collect the results as an array of objects.

Parameters

• options?: Partial<QueryExecutionOptions>

Returns

Promise<any[]>

---

toArrow()

toArrow(options?): Promise<Table<any>>

Collect the results as an Arrow

Parameters

• options?: Partial<QueryExecutionOptions>

Returns

Promise<Table<any>>

See

ArrowTable.

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where()

where(predicate): this

A filter statement to be applied to this query.

The filter should be supplied as an SQL query string. For example:

Parameters

• predicate: string

Returns

this

Example

x > 10
y > 0 AND y < 100
x > 5 OR y = 'test'

Filtering performance can often be improved by creating a scalar index
on the filter column(s).