6.8.1 Getting Started with PGQL

This section provides an example on how to get started with PGQL. It assumes a database realm that has been previously set up (follow the steps in Prepare the Graph Server for Database Authentication). It also assumes that the user has read access to the HR schema.

First, create a graph with employees, departments, and employee works at department, by executing a CREATE PROPERTY GRAPH statement.

Example 6-1 Creating a graph in the graph server (PGX)

The following statement creates a graph in the graph server (PGX)

String statement =
      "CREATE PROPERTY GRAPH hr_simplified "
    + "  VERTEX TABLES ( "
    + "    hr.employees LABEL employee "
    + "      PROPERTIES ARE ALL COLUMNS EXCEPT ( job_id, manager_id, department_id ), "
    + "    hr.departments LABEL department "
    + "      PROPERTIES ( department_id, department_name ) "
    + "  ) "
    + "  EDGE TABLES ( "
    + "    hr.employees AS works_at "
    + "      SOURCE KEY ( employee_id ) REFERENCES employees "
    + "      DESTINATION departments "
    + "      PROPERTIES ( employee_id ) "
    + "  )";
session.executePgql(statement);

/**
 * To get a handle to the graph, execute:
 */
PgxGraph g = session.getGraph("HR_SIMPLIFIED");

/**
 * You can use this handle to run PGQL queries on this graph.
 * For example, to find the department that “Nandita Sarchand” works for, execute:
 */
String query =
    "SELECT dep.department_name "
  + "FROM MATCH (emp:Employee) -[:works_at]-> (dep:Department) "
  + "WHERE emp.first_name = 'Nandita' AND emp.last_name = 'Sarchand' "
  + "ORDER BY 1";
PgqlResultSet resultSet = g.queryPgql(query);
resultSet.print();
+-----------------+
| department_name |
+-----------------+
| Shipping        |
+-----------------+

/**
 * To get an overview of the types of vertices and their frequencies, execute:
 */
String query =
      "SELECT label(n), COUNT(*) "
    + "FROM MATCH (n) "
    + "GROUP BY label(n) "
    + "ORDER BY COUNT(*) DESC";
PgqlResultSet resultSet = g.queryPgql(query);
resultSet.print();

+-----------------------+
| label(n)   | COUNT(*) |
+-----------------------+
| EMPLOYEE   | 107      |
| DEPARTMENT | 27       |
+-----------------------+

/**
  *To get an overview of the types of edges and their frequencies, execute:
  */
 String query =
    "SELECT label(n) AS srcLbl, label(e) AS edgeLbl, label(m) AS dstLbl, COUNT(*) "
  + "FROM MATCH (n) -[e]-> (m) "
  + "GROUP BY srcLbl, edgeLbl, dstLbl "
  + "ORDER BY COUNT(*) DESC";
PgqlResultSet resultSet = g.queryPgql(query);
resultSet.print();

+---------------------------------------------+
| srcLbl   | edgeLbl  | dstLbl     | COUNT(*) |
+---------------------------------------------+
| EMPLOYEE | WORKS_AT | DEPARTMENT | 106      |
+---------------------------------------------+