N1QL Queries from the SDK

You can query for documents in Couchbase using the N1QL query language, a language based on SQL, but designed for structured and flexible JSON documents. Querying can solve typical programming tasks such as finding a user profile by email address, facebook login, or user ID.

Our query service uses N1QL, which will be fairly familiar to anyone who’s used any dialect of SQL. Further resources for learning about N1QL are listed at the bottom of the page. Before you get started you may wish to checkout the N1QL intro page, or just dive in with a query against our travel sample data set. In this case, the one thing that you need to know is that in order to make a Bucket queryable, it must have at least one index defined. You can define a _primary index on a bucket. When a primary index is defined you can issue non-covered queries on the bucket as well.

Use cbq, our interactive Query shell. Open it, and enter the following:

CREATE PRIMARY INDEX ON `travel-sample`

or replace travel-sample with a different Bucket name to build an index on a different dataset.

The default installation places cbq in /opt/couchbase/bin/ on Linux, /Applications/Couchbase Server.app/Contents/Resources/couchbase-core/bin/cbq on OS X, and C:\Program Files\Couchbase\Server\bin\cbq.exe on Microsoft Windows.

Queries & Placeholders

Placeholders allow you to specify variable constraints for an otherwise constant query. There are two variants of placeholders: postional and named parameters. Positional parameters use an ordinal placeholder for substitution and named parameters use variables. A named or positional parameter is a placeholder for a value in the WHERE, LIMIT or OFFSET clause of a query. Note that both parameters and options are optional.

Positional parameter example:
$options = new \Couchbase\QueryOptions();
$options->positionalParameters(["hotel"]);
// NOTE: string is single-quoted to avoid PHP variable substitutions and pass '$1' as is
$result = $bucket->query('SELECT x.* FROM `travel-sample` x WHERE x.`type`=$1 LIMIT 10;', $options);
Named parameter example:
$options = new \Couchbase\QueryOptions();
$options->namedParameters(['type' => "hotel"]);
$result = $bucket->query('SELECT x.* FROM `travel-sample` x WHERE x.`type`=$type LIMIT 10;', $options);

Handling Results

In most cases your query will return more than one result, and you may be looking to iterate over those results:

$options = new \Couchbase\QueryOptions();
$options->positionalParameters(["hotel"]);
$result = $bucket->query('SELECT x.* FROM `travel-sample` x WHERE x.`type`=$1 LIMIT 10;', $options);

foreach($result->rows() as $row) {
    printf("Name: %s, Address: %s, Description: %s\n", $row["name"], $row["address"], $row["description"]);
}

Scan Consistency

Setting a staleness parameter for queries, with scan_consistency, enables a tradeoff between latency and (eventual) consistency.

  • A N1QL query using the default Not Bounded Scan Consistency will not wait for any indexes to finish updating before running the query and returning results, meaning that results are returned quickly, but the query will not return any documents that are yet to be indexed.

  • With Scan Consistency set to RequestPlus, all document changes and index updates are processed before the query is run. Select this when consistency is always more important than performance.

  • For a middle ground, AtPlus is a "read your own write" (RYOW) option, which means it just waits for the new documents that you specify to be indexed, rather than an entire index of multiple documents.

ScanConsisteny (RYOW)
$query = 'SELECT x.* FROM `travel-sample` x WHERE x.`type`="hotel" LIMIT 10';
$opts = new QueryOptions();
$opts->scanConsistency(QueryScanConsistency::REQUEST_PLUS);
$res = $cluster->query($query, $opts);

More granular consistency requirement could be achieved with consistentWith query option, which accepts MutationState object that contains mutations the system must wait for before process the query

// create/update document (mutation)
$res = $collection->upsert("id", ["name" => "somehotel", "type" => "hotel"]);

// create mutation state from mutation results
$state = new MutationState();
$state->add($res);

// use mutation state with query optionss
$opts = new QueryOptions();
$opts->consistentWith($state);
$res = $cluster->query('SELECT x.* FROM `travel-sample` x WHERE x.`type`="hotel" AND x.name LIKE "%hotel%" LIMIT 10', $opts);

Additional Resources

N1QL is not the only query option in Couchbase. Be sure to check that your use case fits your selection of query service.

The Server doc N1QL intro introduces up a complete guide to the N1QL language, including all of the latest additions.

The N1QL interactive tutorial is a good introduction to the basics of N1QL use.