USE Clause
- reference
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.
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.
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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.
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-term ::= 'PRIMARY'? 'KEYS' expr
Synonym: USE KEYS and USE PRIMARY KEYS are synonyms.
| expr |
String of a document key or an array of comma-separated document keys. |
Examples
To try the examples in this section, set the query context to the inventory scope in the travel sample dataset.
For more information, see Query Context.
SELECT *
FROM airport
USE KEYS "airport_1254";[
{
"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"
}
}
]SELECT *
FROM airport
USE KEYS ["airport_1254","airport_1255"];[
{
"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.
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-term ::= 'INDEX' '(' index-ref ( ',' index-ref )* ')'
index-ref ::= index-name? index-type?
| 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. |
| index-type |
USING clause
index-type ::= '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. You can use this hint to specify that the query is a Flex Index query using a Full Text Search index. In Couchbase Server Community Edition, 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
To try the examples in this section, set the query context to the inventory scope in the travel sample dataset.
For more information, see Query Context.
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 route.
SELECT id FROM route
USE INDEX (def_inventory_route_route_src_dst_day USING GSI)
WHERE sourceairport = "SFO"
LIMIT 1;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 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.