USE Clause

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    The USE clause enables you to specify that the query should use particular keys, or a particular index.

    Purpose

    The USE clause is used within the FROM clause. It enables you to provide a hint to the query service, specifying that the query should use particular keys, or a particular index.

    Prerequisites

    For you to select data from a document or keyspace, you must have the query_select privilege on the document or keyspace. For more details about user roles, see Authorization.

    Syntax

    USE KEYS Clause

    Purpose

    You can refer to a document’s unique document key by using the USE KEYS clause. Only documents having those document keys will be included as inputs to a query.

    Syntax

    use-keys-clause ::= USE use-keys-term
    use keys clause
    use-keys-term ::= [ PRIMARY ] KEYS expr
    use keys term
    PRIMARY KEYS

    USE KEYS and USE PRIMARY KEYS are synonyms.

    Arguments

    expr

    String of a document key or an array of comma-separated document keys.

    Examples

    Example 1. Select a single document by its document key
    SELECT *
    FROM `travel-sample`
    USE KEYS "airport_1254";
    Results
    [
      {
        "travel-sample": {
          "airportname": "Calais Dunkerque",
          "city": "Calais",
          "country": "France",
          "faa": "CQF",
          "geo": {
            "alt": 12,
            "lat": 50.962097,
            "lon": 1.954764
          },
          "icao": "LFAC",
          "id": 1254,
          "type": "airport",
          "tz": "Europe/Paris"
        }
      }
    ]
    Example 2. Select multiple documents by their document keys
    SELECT *
    FROM `travel-sample`
    USE KEYS ["airport_1254","airport_1255"];
    Results
    [
      {
        "travel-sample": {
          "airportname": "Calais Dunkerque",
          "city": "Calais",
          "country": "France",
          "faa": "CQF",
          "geo": {
            "alt": 12,
            "lat": 50.962097,
            "lon": 1.954764
          },
          "icao": "LFAC",
          "id": 1254,
          "type": "airport",
          "tz": "Europe/Paris"
        }
      },
      {
        "travel-sample": {
          "airportname": "Peronne St Quentin",
          "city": "Peronne",
          "country": "France",
          "faa": null,
          "geo": {
            "alt": 295,
            "lat": 49.868547,
            "lon": 3.029578
          },
          "icao": "LFAG",
          "id": 1255,
          "type": "airport",
          "tz": "Europe/Paris"
        }
      }
    ]

    USE INDEX clause

    Purpose

    Use the USE INDEX clause to specify the index or indexes to be used as part of the query execution. The query engine attempts to use a specified index if the index is applicable for the query.

    In Couchbase Server 6.6 and later, you can omit the index name and just specify the index type. In this case, the query service considers all the available indexes of the specified type.

    Syntax

    use-index-clause ::= USE use-index-term
    use index clause
    use-index-term ::= INDEX '(' index-ref [ ',' index-ref ]* ')'
    use index term
    index-ref ::= [ index-name ] [ index-type ]
    index ref

    Arguments

    index-name

    [Optional] String or expression representing an index to be used for the query.

    This argument is optional; if omitted, the query engine considers all available indexes of the specified index type.

    USING clause

    index-type ::= USING ( GSI | FTS )
    'USING' ( 'GSI' | 'FTS' )

    Specifies which index form to use.

    USING GSI

    A Global Secondary Index, which lives on an index node and can possibly be separate from a data node.

    USING FTS

    A Full Text Search index, for use with queries containing Search functions. In Couchbase Server 6.6 Enterprise Edition and later, you can use this hint to specify that the query is a Flex Index query using a Full Text Search index. In Couchbase Server 6.6 Community Edition and later, this hint is ignored if the query does not contain a Search function.

    This clause is optional; if omitted, the default is USING GSI.

    Examples

    Example 3. Use a specified Global Secondary Index

    Create an index of airlines and destination airports, and then use it in a query for flights originating in San Francisco.

    CREATE INDEX idx_destinations
    ON `travel-sample` (airlineid, airline, destinationairport)
    WHERE type="route";
    SELECT airlineid, airline, sourceairport, destinationairport
    FROM `travel-sample` USE INDEX (idx_destinations USING GSI)
    WHERE sourceairport = "SFO";
    Example 4. Use any suitable Full Text Search index

    Specify that the query service should prefer an FTS index, without specifying the index by name. To qualify for this query, there must be an FTS index on state and type, using the keyword analyzer. (Or alternatively, an FTS index on state, with a custom type mapping on "hotel".)

    SELECT META().id
    FROM `travel-sample` USE INDEX (USING FTS)
    WHERE type = "hotel" AND (state = "Corse" OR state = "California");

    All FTS indexes are considered. If a qualified FTS index is available, it is selected for the query. If none of the available FTS indexes are qualified, the available GSI indexes are considered instead.