By creating a view, path expressions (such as $path.$siteno) become columns in the view allowing the user to specify WHERE clauses on those columns without being aware that the underlying table contains complex path expressions.
The names given to the columns in the view are case insensitive. Although shown in mixed case, they can be referenced in SQL queries using any mix of case desired.
The examples use a sample river flow data set. To use your own data, replace the table and column names, and authorization object. See Variable Substitutions for Examples for the credentials and location values for the sample data set.
- To run NOS-related commands, log on to the database as a user with the required privileges.
- If it does not exist, create the foreign table or ask your database administrator to create the foreign table called riverflow_parquet_path. See: Filtering External Parquet Data From a Foreign Table.
Create a view of the foreign table called riverflow_parquet:
CREATE VIEW riverflowview_parquet AS ( SELECT CAST($path.$siteno AS CHAR(10)) TheSite, CAST($path.$year AS CHAR(4)) TheYear, CAST($path.$month AS CHAR(2)) TheMonth, CAST(SUBSTR($path.$day, 1, 2) AS CHAR(2)) TheDay, Flow, GageHeight GageHeight1, Precipitation, GageHeight2 FROM riverflow_parquet_path);