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SORT operation in AQL

The SORT operation allows you to specify one or multiple sort criteria and directions to control the order of query results or the elements of arrays

Syntax

The general syntax is:

SORT expression direction

Usage

The SORT operation sorts the already produced intermediate results of the current block. For example, the following query sorts by lastName (in ascending order), then firstName (in ascending order), then by id (in descending order):

FOR u IN users
  SORT u.lastName, u.firstName, u.id DESC
  RETURN u

Specifying the direction is optional. The default (implicit) direction for a sort expression is the ascending order. To explicitly specify the sort direction, the keywords ASC (ascending) and DESC (descending) can be used. Multiple sort criteria can be separated using commas. In this case, the direction is specified for each expression separately.

The following example first sorts documents by lastName in ascending order and then by firstName in ascending order.

SORT doc.lastName, doc.firstName

The following example first sorts documents by lastName in descending order and then by firstName in ascending order.

SORT doc.lastName DESC, doc.firstName

The following example first sorts documents by lastName in ascending order and then by firstName in descending order.

SORT doc.lastName, doc.firstName DESC

When iterating over a collection, the order of documents is always undefined unless an explicit sort order is defined with a SORT operation.

If the values you sort by are not unique, the order among tied documents is undefined and you may want to sort by another attribute to break ties. If the application has a preferred attribute that indicates the order of documents with the same value, then use this attribute. If there is no such attribute, you can still achieve a stable sort by using the _id system attribute as it is unique and present in every document.

FOR u IN users
  SORT u.firstName, u._id // break name ties with the document ID
  RETURN u

Constant SORT expressions can be used to indicate that no particular sort order is desired.

SORT null

Constant SORT expressions are optimized away by the AQL optimizer during optimization, but specifying them explicitly may enable further optimizations if the optimizer does not need to take into account any particular sort order. This is especially the case after a COLLECT statement, which is supposed to produce a sorted result. Specifying an extra SORT null after the COLLECT statement allows to AQL optimizer to remove the post-sorting of the collect results altogether. Also see COLLECT option method.

In case of a sequence of SORT operations, the last one is always the one that is performed unless a previous SORT expression is more accurate. If the optimization rules remove-redundant-sorts and remove-redundant-sorts-2 are deactivated in the query’s execution, then the last SORT is always the one that wins, despite the accuracy. For example, consider the following query with multiple consecutive SORT operations:

FOR friend IN friends
  SORT friend.friend.name, friend.id, friend.age 
  SORT friend.age, friend.id
  SORT friend.age
  RETURN friend

If the optimization rules mentioned above are deactivated, then the last SORT becomes operative and the collection is sorted by friend.age. If the optimization rules are active, then the second SORT becomes operative because it covers the same friend.age attribute and additionally sorts by another attribute in case of ties, making it more accurate. However, if the attributes in the second SORT expression are in opposite order, as in SORT friend.id, friend.age, then the last SORT is operative.

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