Using EXTRACT
You can use EXTRACT() and DATE_PART() to easily create new fields in your queries by extracting sub-fields from a source timestamp field.
Now suppose you want to produce a predictive model that will help forecast DVD rental activity by day of the week. You could use the EXTRACT() function with the dow field identifier in our query to create a new field called dayofweek as a sub-field of the rental_date column from the rental table.
You can COUNT() the number of records in the rental table for a given date range and aggregate by the newly created dayofweek column.
Questo esercizio fa parte del corso
Functions for Manipulating Data in PostgreSQL
Esercizio pratico interattivo
Prova a risolvere questo esercizio completando il codice di esempio.
SELECT
-- Extract day of week from rental_date
___(___ ___ ___) AS dayofweek
FROM rental
LIMIT 100;