In order to work with EQL, you need to understand the following
concepts.
- Attribute: An
attribute is the basic unit of a record schema. Attributes describe records in
the Dgraph. From the point of view of assignments on records, an attribute can
be either:
- Single-assign
attribute: An attribute for which a record may have only one value. For
example, because a book has only one price, the Price attribute would be
single-assign. Single-assign attributes are of the atomic data type (such as
mdex:string and
mdex:double).
- Multi-assign
attribute: An attribute for which a record may have more than one value.
For example, because a book may have more than one author, the Author attribute
would be multi-assign. Multi-assign attributes are of the set data type (such
as
mdex:string-set and
mdex:double-set). They are represented in EQL by
sets (see
Sets and Multi-assign Data).
- Record: The
fundamental unit of data in the Dgraph. Records are assigned attribute values.
An assignment indicates that a record has a value for an attribute. A record
typically has assignments from multiple attributes. Records in collections can
include multiple assignments to the same attribute, as can records in EQL
results.
- Collection: The full body of Dgraph
application records is contained in one or more collections (called
data sets in Studio). Thus, Dgraph data is collection-based
rather than table-based. By using a
FROM clause in your statement, you specify a named
state. This serves as the record source for your query. (The named state
references a collection name and the Dgraph database, for the data set.)
Alternatively, theFROM clause can specify a previously-defined
statement as the record source. Note that a
FROM clause is mandatory in an EQL statement.
- Statement: A unit of
EQL that computes related or independent analytics results. In EQL, a statement
starts with
DEFINE or
RETURN and ends with a semi-colon if it is between
statements (the semi-colon is optional on the last statement). The statement
also includes a mandatory
SELECT clause and, optionally, some other clause(s).
- Result: Query results
are a collection of statement results; statement results are a collection of
records.
- Intermediate
results: Results from
RETURN statements can also be used as intermediate
results for further processing by other statements.
- Returned results:
Set of matching values returned by the query or statement.
- Query: A request sent
to the Dgraph Gateway (and ultimately to the Dgraph). In general, a query
consists of multiple statements.
