Purpose

Each GRAPH_TABLE starts with a graph reference that references the graph to perform the pattern matching on.

Prerequisites

To query a property graph, you must have READ or SELECT object privilege on the graph. Note that you do not require READ or SELECT object privilege on the tables or materialized views that underlie the graph.

To issue an Oracle Flashback Query using the graph_ref_as_of_clause in GRAPH_TABLE, you must additionally have FLASHBACK object privilege on the tables and materialized views that underlie the graph. This is needed only for those tables and views that are accessed by the query, based on the specified graph pattern and label expressions used therein. Alternatively, you must have FLASHBACK ANY TABLE system privilege.

Syntax

graph_reference::=

Description of the illustration graph_reference.eps

graph_name::=

Description of the illustration graph_name.eps

graph_ref_as_of_clause::=

Description of the illustration graph_ref_as_of_clause.eps

Semantics

A graph name may be qualified with a schema name to allow for querying graphs created by other users. Furthermore, you can specify the graph_ref_as_of_clause clause to retrieve the result of the graph query at a particular change number (SCN) or timestamp. If you specify SCN, then expr must evaluate to a number. If you specify TIMESTAMP, then expr must evaluate to a timestamp value. In either case, expr cannot evaluate to NULL.

Example 1

The following query counts the number of persons in the students_graph owned by user scott:

SELECT COUNT(*)
FROM GRAPH_TABLE ( scott.students_graph
  MATCH (a IS person)
  COLUMNS (a.name)
);

The output is:

  COUNT(*)
----------
      4

Example 2

The following example queries a graph at two different timestamps. It first inserts a new row into the university table that underlies the students_graph. It then queries versions of the graph before and after the insertion.

INSERT INTO university (name) VALUES ('u3');

SELECT COUNT(*)
FROM GRAPH_TABLE (
  students_graph
  MATCH (u IS university)
  COLUMNS (u.*)
);

SELECT COUNT(*)
FROM GRAPH_TABLE (
  students_graph AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '2' MINUTE)
  MATCH (u IS university)
  COLUMNS (u.*)
);

DELETE FROM university WHERE name = 'u3';

The output of the first query is:

  COUNT(*)
----------
         3

The output of the second query is:

   COUNT(*)
----------
         2

Note: this example assumes that the second SELECT query is run at least two minutes after the graph was created and within two minutes after running the INSERT statement, otherwise the output is different.