drill

734c4607 - DRILL-3988: Expose Drill built-in functions & UDFs in a system table (#1483)

DRILL-3988: Expose Drill built-in functions & UDFs in a system table (#1483) This commit exposes available SQL functions in Drill and also detects UDFs that have been dynamically loaded into Drill. An example is shown below for 2 UDFs dynamically loaded into the cluster, along side the existing built-in functions that come with Drill. ``` 0: jdbc:drill:schema=sys> select source, count(*) as functionCount from sys.functions group by source; +-----------------------------------------+----------------+ | source | functionCount | +-----------------------------------------+----------------+ | built-in | 2704 | | simple-drill-function-1.0-SNAPSHOT.jar | 12 | | drill-url-tools-1.0.jar | 1 | +-----------------------------------------+----------------+ 3 rows selected (0.209 seconds) ``` The system table exposes information as shown. The UDF is initialized, making the `returnType` available. The `random(FLOAT8-REQUIRED,FLOAT8-REQUIRED)` function is an example of a UDF that has overloaded arguments (see `signature`). The `url_parse(VARCHAR-REQUIRED)` function is another example of an initialized UDF. Rest are built-in functions that meet the query's filter criteria. ``` 0: jdbc:drill:schema=sys> select * from sys.functions where name like 'random' or name like '%url%'; +-------------+----------------------------------+-------------+-----------------------------------------+ | name | signature | returnType | source | +-------------+----------------------------------+-------------+-----------------------------------------+ | parse_url | VARCHAR-REQUIRED | LATE | built-in | | random | | FLOAT8 | built-in | | random | FLOAT8-REQUIRED,FLOAT8-REQUIRED | FLOAT8 | simple-drill-function-1.0-SNAPSHOT.jar | | url_decode | VARCHAR-REQUIRED | VARCHAR | built-in | | url_encode | VARCHAR-REQUIRED | VARCHAR | built-in | | url_parse | VARCHAR-REQUIRED | LATE | drill-url-tools-1.0.jar | +-------------+----------------------------------+-------------+-----------------------------------------+ 6 rows selected (0.619 seconds) ```