OData $orderby syntax in Azure AI Search
In Azure AI Search, the $orderby parameter specifies a custom sort order for search results. This article describes the OData syntax of $orderby and provides examples.
Field path construction and constants are described in the OData language overview in Azure AI Search. For more information about sorting behaviors, see Ordering results.
Syntax
The $orderby parameter accepts a comma-separated list of up to 32 order-by clauses. The syntax of an order-by clause is described by the following EBNF (Extended Backus-Naur Form):
order_by_clause ::= (field_path | sortable_function) ('asc' | 'desc')?
sortable_function ::= geo_distance_call | 'search.score()'
An interactive syntax diagram is also available:
Note
See OData expression syntax reference for Azure AI Search for the complete EBNF.
Each clause has sort criteria, optionally followed by a sort direction (asc for ascending or desc for descending). If you don't specify a direction, the default is ascending. If there are null values in the field, null values appear first if the sort is asc and last if the sort is desc.
The sort criteria can either be the path of a sortable field or a call to either the geo.distance or the search.score functions.
For string fields, the default ASCII sort order and default Unicode sort order will be used. By default, sorting is case sensitive but you can use a normalizer to preprocess the text before sorting to change this behavior. You can also use an asciifolding normalizer to convert non-ASCII characters to their ASCII equivalent, if one exists.
If multiple documents have the same sort criteria and the search.score function isn't used (for example, if you sort by a numeric Rating field and three documents all have a rating of 4), ties will be broken by document score in descending order. When document scores are the same (for example, when there's no full-text search query specified in the request), then the relative ordering of the tied documents is indeterminate.
You can specify multiple sort criteria. The order of expressions determines the final sort order. For example, to sort descending by score, followed by Rating, the syntax would be $orderby=search.score() desc,Rating desc.
The syntax for geo.distance in $orderby is the same as it is in $filter. When using geo.distance in $orderby, the field to which it applies must be of type Edm.GeographyPoint and it must also be sortable.
The syntax for search.score in $orderby is search.score(). The function search.score doesn't take any parameters.
Examples
Sort hotels ascending by base rate:
$orderby=BaseRate asc
Sort hotels descending by rating, then ascending by base rate (remember that ascending is the default):
$orderby=Rating desc,BaseRate
Sort hotels descending by rating, then ascending by distance from the given coordinates:
$orderby=Rating desc,geo.distance(Location, geography'POINT(-122.131577 47.678581)') asc
Sort hotels in descending order by search.score and rating, and then in ascending order by distance from the given coordinates. Between two hotels with identical relevance scores and ratings, the closest one is listed first:
$orderby=search.score() desc,Rating desc,geo.distance(Location, geography'POINT(-122.131577 47.678581)') asc