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.

    In Couchbase Server 7.1 and later, you can also supply an index hint within a specially-formatted hint comment. Note that you cannot specify an index hint for the same keyspace using both the USE clause and a hint comment. If you do this, the USE clause and the hint comment are both marked as erroneous and ignored by the optimizer.

    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.

    There is no optimizer hint equivalent to this clause.

    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`.inventory.airport
    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`.inventory.airport
    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.

    If necessary, 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.

    In Couchbase Server 7.1 and later, this clause is equivalent to the INDEX and INDEX_FTS optimizer hints. For more details, refer to Keyspace Hints.

    If you attempt to use an index which is still scheduled for background creation, the request fails.

    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

    This example uses the index def_inventory_route_route_src_dst_day, which is installed with the travel-sample bucket.

    The following query hints that the optimizer should select the specified index for the keyspace `travel-sample`.inventory.route.

    INDEX hint
    SELECT id FROM `travel-sample`.inventory.route
    USE INDEX (def_inventory_route_route_src_dst_day USING GSI)
    WHERE sourceairport = "SFO"
    LIMIT 1;
    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`.inventory.hotel USE INDEX (USING FTS)
    WHERE 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.