Syntax (BNF)

The basic structure of a query is an ordered list of statements. The result of a query is a set of named record sets (one per statement). 

<Query>        ::=  <Statements>
<Statements>   ::=  <Statement> [; <Statements>]

A statement defines a record set by specifying:

  1. A name for the resulting record set.

  2. What properties (or derived properties) its records should contain (SELECTs).

  3. The input record set (FROM).

  4. A filter to apply to that input (WHERE).

  5. A way to group input records (a mapping from input records to output records, GROUP BY).

  6. A filter to apply to output records (HAVING).

  7. A way to order the output records (ORDER BY).

  8. A way to page through the output records (return only a subset of the output, PAGE). 

<Statement>    ::=  (DEFINE | RETURN) <Key> AS <Select>
                       [<From>]
                       [<Where>]
                       [<GroupBy>]
                       [<Having>]
                       [<OrderBy>]
                       [<Page>]

A statement includes a list of assignments that compute the derived properties populated into the resulting records: 

<Select>       ::=  SELECT <Assigns>
<Assigns>      ::=  <Assign> [, <Assigns>]
<Assign>       ::=  <Expr> AS <Key>

A statement’s input record set is either the result of a previous statement, the navigation state’s records (NavStateRecords), or the Dgraph’s base records (AllBaseRecords). The omission of the FROM clause implies FROM NavStateRecords. 

<From>         ::=  FROM <Key>
               ::=  FROM NavStateRecords
               ::=  FROM AllBaseRecords

As in SQL, an optional WHERE clause represents a pre-filter on inbound records, and an optional HAVING clause represents a post-filter on the output records: 

<Where>        ::=  WHERE <Filter>
<Having>       ::=  HAVING <Filter>

Input records need to be mapped to output records for the purposes of populating derived values in the output records. The input records provide the values used in expressions and Where filters.

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