Supported since 5.0.2.
Through the Presto (opens new window) connector, Ontop is able to construct VKGs on Presto databases.
# Limitations & Exceptions
Presto does not provide information about integrity constraints. Make sure to provide this information in order to avoid very inefficient queries. We recommend using lenses for this purpose.
- Accessing struct fields with the "dot operator" is not supported (see below).
# Database Connection
The following shows the content of a sample
.properties file that can be used to connect Ontop to Presto:
jdbc.url = jdbc:presto://localhost:8080/defaultdatabase jdbc.user = user jdbc.password = password jdbc.driver = com.facebook.presto.jdbc.PrestoDriver
In case Presto is set up without authentication, the
jdbc.password lines can also be left out.
# Nested Type Support
Ontop implements explicit compatibility with the Presto array type
array(t). When used with the flatten lens, it is able to automatically infer the type of the result column.
The flatten lens cannot be used on arrays stored as JSON-encoded columns in the database. For such use cases, the column first has to be converted to an array type.
# Struct Access
In Presto, individual
ROW objects can be accessed by SQL expressions using the "dot operator" on the
ROW column. In Ontop, this feature is not currently supported.
Should any of their elements still be required, then a workaround can be performed by first transforming the struct into a JSON object and then accessing it using JSON functions.
JSON_EXTRACT(CAST(my_struct AS JSON), '$.my_attribute')
MAP objects can be accessed using the
 operator, as in
SELECT my_map['my_attribute'] FROM ...