5.1.3 Accessing Label Properties

You can access a property inside a graph element pattern, in the out-of-line WHERE clause or in the COLUMNS clause.

Consider the following graph element pattern where a is a graph element variable and name is a property name:

(a IS person WHERE a.name='John')

You can then reference the property in the WHERE clause inside the graph element pattern as a.name. This means a.name references the property name of the graph element bound to the graph pattern variable a.

Also, the following conditions apply when accessing a property:

• The property name is part of at least one table that satisfies the label expression.
• A graph variable name must always be used to access a property.
• At the time of query compilation, certain type checking rules apply for the vertex or edge table properties. See Type Compatibility Rules for Determining Property Types for more information.

The following examples describe a few scenarios for determining property types when querying SQL property graphs. Note that Example 5-1 to Example 5-3 refer to the SQL property graph definition for g1 which contains height as a shared property across different labels.

Example 5-1 Determining the Property Type for a Single Label

The data type for a.height in the following query is FLOAT:

SELECT * FROM GRAPH_TABLE (g1
MATCH
(a IS person)
COLUMNS (a.height)
);

The query output is as shown:

HEIGHT
----------
       1.8
      1.65
      1.75
       1.7

Example 5-2 Determining Union Compatible Property Type for Two Different Labels

The data type for a.height in the following query is the union compatible type between FLOAT and BINARY_DOUBLE:

SELECT * FROM GRAPH_TABLE (g1
MATCH
(a IS person|t3)
COLUMNS (a.height)
);

The query output is as shown:

    HEIGHT
----------
  1.8E+000
 1.65E+000
 1.75E+000
  1.7E+000
  1.8E+000
 1.65E+000

In the SQL property graph g1, the property type for height associated with the labels person and t3 is FLOAT and BINARY_DOUBLE respectively. BINARY_DOUBLE takes precedence over FLOAT and hence the resulting output property type for a.height is BINARY_DOUBLE.

Example 5-3 No Union Compatible Property Type for Two Different Labels

Error is thrown for the following query as the data type for a.height is not union compatible across the tables, person (FLOAT) and t2 (VARCHAR):

SELECT * FROM GRAPH_TABLE (g1
  MATCH
   (a IS person|t2)
  COLUMNS (a.height)
  );

On execution. the preceding query throws the error - ORA-01790: expression must have same datatype as corresponding expression

Example 5-4 Determining Union Compatible Property Type for Shared Labels

Consider the SQL property graph definition for g3 which uses a shared label (t) that is associated with a shared property name (height).

When querying g3, the data type for a.height in the following SQL graph query is BINARY_DOUBLE:

SELECT * FROM GRAPH_TABLE (g3
MATCH
(a IS t)
COLUMNS (a.height)
);

The query output is a union of the property columns across all the graph element tables sharing the label. Also, the property type is BINARY_DOUBLE as per the Type Compatibility Rules for Determining Property Types:

    HEIGHT
----------
  1.8E+000
 1.65E+000
 1.75E+000
  1.7E+000
  1.8E+000
 1.65E+000