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  3. Functions for Manipulating Data in PostgreSQL

Exercise

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.

Instructions 1/2

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  • Get the day of the week from the rental_date column.