Query external data
This topic guides you through querying data from external data sources by using external catalogs.
Prerequisites
External catalogs are created based on external data sources. For information about supported types of external catalogs, see Catalog.
Procedure
-
Connect your StarRocks cluster.
- If you use the MySQL client to connect the StarRocks cluster, you go to
default_catalog
by default after connecting. - If you use JDBC to connect the StarRocks cluster, you can go directly to the destination database in the default catalog by specifying
default_catalog.db_name
when connecting.
- If you use the MySQL client to connect the StarRocks cluster, you go to
-
(Optional) Execute the following statement to view all the catalogs and find the external catalog you have created. See SHOW CATALOGS to check the output of this statement.
SHOW CATALOGS;
-
(Optional) Execute the following statement to view all the databases in the external catalog. See SHOW DATABASES to check the output of this statement.
SHOW DATABASES FROM catalog_name;
-
(Optional) Execute the following statement to go to the destination database in the external catalog.
USE catalog_name.db_name;
-
Query external data. For more usages of the SELECT statement, see SELECT.
SELECT * FROM table_name;
If you do not specify the external catalog and database in the preceding steps, you can directly specify them in a select query.
SELECT * FROM catalog_name.db_name.table_name;
Examples
If you already created a Hive catalog named hive1
and want to use hive1
to query data from hive_db.hive_table
of an Apache Hive™ cluster, you can perform one of the following operations:
USE hive1.hive_db;
SELECT * FROM hive_table limit 1;
Or
SELECT * FROM hive1.hive_db.hive_table limit 1;
References
To query data from your StarRocks cluster, see Default catalog.