6.20. PostgreSQL Connector
The PostgreSQL connector allows querying and creating tables in an external PostgreSQL database. This can be used to join data between different systems like PostgreSQL and Hive, or between different PostgreSQL instances.
Configuration
To configure the PostgreSQL connector, create a catalog properties file
in etc/catalog named, for example, postgresql.properties, to
mount the PostgreSQL connector as the postgresql catalog.
Create the file with the following contents, replacing the
connection properties as appropriate for your setup:
connector.name=postgresql
connection-url=jdbc:postgresql://example.net:5432/database
connection-user=root
connection-password=secret
Multiple PostgreSQL Databases or Servers
The PostgreSQL connector can only access a single database within a PostgreSQL server. Thus, if you have multiple PostgreSQL databases, or want to connect to multiple PostgreSQL servers, you must configure multiple instances of the PostgreSQL connector.
To add another catalog, simply add another properties file to etc/catalog
with a different name, making sure it ends in .properties. For example,
if you name the property file sales.properties, Presto creates a
catalog named sales using the configured connector.
Decimal Type Handling
DECIMAL types with precision larger than 38 can be mapped to a Presto DECIMAL
by setting the decimal-mapping configuration property or the decimal_mapping session property to
allow_overflow. The scale of the resulting type is controlled via the decimal-default-scale
configuration property or the decimal-rounding-mode session property. The precision is always 38.
By default, values that require rounding or truncation to fit will cause a failure at runtime. This behavior
is controlled via the decimal-rounding-mode configuration property or the decimal_rounding_mode session
property, which can be set to UNNECESSARY (the default),
UP, DOWN, CEILING, FLOOR, HALF_UP, HALF_DOWN, or HALF_EVEN
(see RoundingMode).
Array Type Handling
The PostgreSQL array implementation does not support fixed dimensions whereas Presto
support only arrays with fixed dimensions.
You can configure how the PostgreSQL connector handles arrays with the postgresql.array-mapping configuration property in your catalog file
or the array_mapping session property.
The following values are accepted for this property:
DISABLED(default): array columns are skipped.AS_ARRAY: array columns are interpreted as PrestoARRAYtype, for array columns with fixed dimensions.AS_JSON: array columns are interpreted as PrestoJSONtype, with no constraint on dimensions.
Querying PostgreSQL
The PostgreSQL connector provides a schema for every PostgreSQL schema.
You can see the available PostgreSQL schemas by running SHOW SCHEMAS:
SHOW SCHEMAS FROM postgresql;
If you have a PostgreSQL schema named web, you can view the tables
in this schema by running SHOW TABLES:
SHOW TABLES FROM postgresql.web;
You can see a list of the columns in the clicks table in the web database
using either of the following:
DESCRIBE postgresql.web.clicks;
SHOW COLUMNS FROM postgresql.web.clicks;
Finally, you can access the clicks table in the web schema:
SELECT * FROM postgresql.web.clicks;
If you used a different name for your catalog properties file, use
that catalog name instead of postgresql in the above examples.
PostgreSQL Connector Limitations
The following SQL statements are not yet supported: