5.4 Vertex and Edge Identifiers

You can uniquely identify each vertex and edge in a SQL property graph with the VERTEX_ID and EDGE_ID operators, respectively, in a SQL graph query.

Graph element identifiers are based on the key value defined for the graph element tables. Therefore, it is important to note the following:

• Graphs in TRUSTED mode may produce duplicate identifiers for different vertices if some key columns do not have a UNIQUE constraint.
• Graphs in ENFORCED mode are guaranteed to always produce unique identifiers.

The VERTEX_ID and EDGE_ID operators can be used in any expression appearing in the COLUMNS or WHERE clause in a SQL graph query.

Note:

In order to use the VERTEX_ID and EDGE_ID operators, you must ensure that you have the READ or SELECT privilege on both the property graph object and its underlying database tables.

The input to the VERTEX_ID operator is a single vertex graph pattern variable coming from a matched vertex pattern as shown:

MATCH (v) COLUMNS(VERTEX_ID(v) AS v_id)

Similarly, the EDGE_ID operator takes as input a single edge graph pattern variable coming from a matched edge pattern as shown:

MATCH (v1)-[e]->(v2) COLUMNS(EDGE_ID(e) AS e_id)

The output of these operators is a vertex or an edge identifier of JSON data type. The following shows an example of a JSON output describing the vertex identifier:

{
  "GRAPH_OWNER": "GRAPHUSER",
  "GRAPH_NAME": "STUDENTS_GRAPH",
  "ELEM_TABLE": "PERSONS",
  "KEY_VALUE": {
    "PERSON_ID": 1
  }
}

In the preceding JSON output:

• GRAPH_OWNER: Owner of the property graph object
• GRAPH_NAME: Name of the property graph object
• ELEM_TABLE: Name of the vertex table
• KEY_VALUE: Name and value of the key column

The same list of JSON output fields apply to an edge identifier also. However, the ELEM_TABLE field represents the name of an edge table. Also, all operations that can be performed on a JSON data type can be performed on the vertex and edge identifiers.

See Example 5-20 for more information.

VERTEX_EQUAL and EDGE_EQUAL Predicates

The VERTEX_EQUAL and EDGE_EQUAL predicates can be used to, respectively, compare two vertex and edge identifiers and return TRUE if they are equal.

The inputs to the VERTEX_EQUAL predicate are two vertex graph pattern variables. Similarly for EDGE_EQUAL, both inputs must be edge graph pattern variables. These predicates can be used in the WHERE clause in a SQL graph query.

See Example 5-21 for more information.