SELECT

The SELECT operation, once executed, retrieves documents from a collection and uses clauses like WHERE to specify conditions for filtering the documents to return.

DQL currently only supports the SELECT * operation for document retrieval. With SELECT *, all responses result in full documents.

Expect more advanced SELECT capabilities in upcoming DQL releases. For more information, see DQL Roadmap Functionality.

SELECT * Statements

The following syntax outlines the basic structure and optional clauses you can use within your SELECT statements to specify your conditions for retrieval:

DQL

SELECT *
FROM your_collection_name
[WHERE condition]
[ORDER BY orderby_expression_1, orderby_expression_2, ... [ASC|DESC]]
[LIMIT limit_value]
[OFFSET number_of_documents_to_skip]

For instance, retrieve all documents in the cars collection WHERE the color property is set to the value ‘blue’ :

DQL

SELECT * FROM cars WHERE color = 'blue'

To perform a SELECT and receive all document fields, including an embedded MAP:

Clauses for Filtering

The following table provides an overview of the different clauses you can use to define specific conditions and calculations within your DQL SELECT statements to provide more granular control over your queries:

Clause	Description
FROM	The required clause specifying the collection containing the documents for retrieval. (See FROM)
WHERE	Applies filtering conditions to restrict the documents included in the result set. (See WHERE)
ORDER BY	Specifies the sorting order of the result set based on one or more expressions. (See ORDER BY)
LIMIT	Restricts the number of documents included in the result set. (See LIMIT)
OFFSET	Skips a specific number of documents before returning the result set. (See OFFSET)

FROM

Required in each SELECT statement you write in DQL, the FROM element identifies the collection for document retrieval.

DQL

SELECT *
FROM your_collection_name

For example, a SELECT statement querying documents from the cars collection:

DQL

SELECT * FROM cars

WHERE

The WHERE clause filters data based on either an expression or a set of conditions that narrow the result set returned to you:

DQL

SELECT *
FROM your_collection_name
WHERE [condition]

For example, here is a basic SELECT statement querying documents from the cars collection based on a given address:

DQL

SELECT * FROM cars
WHERE location.address = '123 Main St, San Francisco, CA 98105'

To demonstrate a more complex query, here is a SELECT statement that queries using multiple expressions and logical operators to further refine the criteria for document retrieval:

DQL

SELECT * FROM cars
WHERE color = 'blue' AND features.trim = 'Standard' OR features.mileage > 10000

ORDER BY

With the ORDER BY clause, if you’d like, you can integrate calculations or expressions in your SELECT statement. Then sort the resulting documents to return in either ascending (ASC) or descending (DESC) alphabetical order:

DQL

SELECT *
FROM your_collection_name
ORDER BY expression_1, expression_2, ... [ASC|DESC]

For example, here is a simple SELECT statement that uses the ORDER BY clause to query and sort documents from the cars collection in descending (DESC) alphabetical order based on the field value set for the color property:

DQL

SELECT *
FROM cars ORDER BY color DESC

In this syntax:

• your_collection_name is the name of the collection from which you want to retrieve the data.
• expression_1, expression_2, ... are the expressions evaluated to sort the result. Expressions are resolved in order.
• [ASC|DESC] is an optional parameter that specifies the sort order. If omitted, the default sort order is ascending (ASC). To sort in descending order, you can specify DESC.

Example

In this example, the result set from the query will be sorted in descending order based on the values in the field:

DQL

-- Sort by a given field_name
SELECT *
FROM your_collection_name
ORDER BY field_name DESC

For instance, here "blue" cars return first and other cars sort by the natural order in the collection:

DQL

SELECT *
FROM cars
ORDER BY color = 'blue'

Sort Order by Object Type

In DQL, the hierarchy for comparing and sorting objects varies based on the following criteria:

• If ascending (ASC) order operations:
  • boolean
  • number
  • binary
  • string
  • array
  • object
  • null
  • missing
• If descending (DESC) order operations, sorting order is reversed:
  • missing
  • null
  • object
  • array
  • string
  • binary
  • number
  • boolean
• If evaluating values, true results are prioritized and ordered first followed by false results.

Expressing Sort Order

Unless explicitly defined as DESC in your query, Ditto defaults to sorting in ascending (ASC). So, if you want to sort in ascending order, you do not have to express that in your query.

LIMIT

The LIMIT clause is used to restrict the number of documents returned by a query, allowing you to specify a maximum limit on the number of documents to be included in the result set:

DQL

SELECT *
FROM your_collection_name
LIMIT limit_value

In this syntax:

• your_collection_name is the name of the collection from which you want to retrieve the data.
• limit_value is the maximum number of documents you want to include in the result set.

For example, only return the first 10 documents from the your_collection_name collection:

DQL

SELECT *
FROM your_collection_name
LIMIT 10

OFFSET

The OFFSET clause is used to specify the number of records to skip before starting to return documents from the query result:

DQL

SELECT *
FROM your_collection_name
OFFSET number_of_items_to_skip

In this syntax:

• your_collection_name is the name of the collection from which you want to retrieve the data.
• number_of_items_to_skip is the number of items before returning the result set.

Using OFFSET with LIMIT is a common way to utilize OFFSET; for example:

DQL

SELECT *
FROM your_collection_name
LIMIT 10
OFFSET 10