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

1. 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.

2. (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;

3. (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;

4. (Optional) Execute the following statement to go to the destination database in the external catalog.

   USE catalog_name.db_name;

5. 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.