Using Custom Functions in Queries

Nov 2, 2018

When you issue a query with a custom function to Drill, Drill searches the classpath for the function that matches the request in the query. Once Drill locates the function for the request, Drill processes the query and applies the function during processing.

Your Drill installation includes sample files in the Drill classpath. One sample file, employee.json, contains some fictitious employee data that you can query with a custom function.

Simple Function Example

This example uses the myaddints simple function in a query on the employee.json file.

If you issue the following query to Drill, you can see all of the employee data within the employee.json file:

0: jdbc:drill:zk=local> SELECT * FROM cp.`employee.json`;

The query returns the following results:

| employee_id | full_name    | first_name | last_name  | position_id | position_title          |  store_id  | department_id | birth_da |
+-------------+------------+------------+------------+-------------+----------------+------------+---------------+----------+-----------
| 1101        | Steve Eurich | Steve      | Eurich     | 16          | Store Temporary Checker | 12         | 16            |
| 1102        | Mary Pierson | Mary       | Pierson    | 16          | Store Temporary Checker | 12         | 16            |
| 1103        | Leo Jones    | Leo        | Jones      | 16          | Store Temporary Checker | 12         | 16            |
…

Since the postion_id and store_id columns contain integers, you can issue a query with the myaddints custom function on these columns to add the integers in the columns.

The following query tells Drill to apply the myaddints function to the position_id and store_id columns in the employee.json file:

0: jdbc:drill:zk=local> SELECT myaddints(CAST(position_id AS int),CAST(store_id AS int)) FROM cp.`employee.json`;

Since JSON files do not store information about data types, you must apply the CAST function in the query to tell Drill that the columns contain integer values.

The query returns the following results:

+------------+
|   EXPR$0   |
+------------+
| 28         |
| 28         |
| 36         |
+------------+
…