Using date functions on strings

There are several useful functions that act specifically on date or datetime fields. For example:

DATE_TRUNC('month', date) truncates each date to the first day of the month.
DATE_PART('year', date) outputs the year, as an integer, of each date value.

In general, the arguments for both functions are ('period', field), where period is a date or time interval, such as 'minute', 'day', or 'decade'.

In this exercise, your goal is to test out these date functions on the country_stats table, specifically by outputting the decade of each year using two separate approaches. To run these functions, you will need to use CAST() function on the year field.

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Reporting in SQL

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Instrucciones del ejercicio

Pulling from the country_stats table, select the decade using two methods: DATE_PART() and DATE_TRUNC.
Convert the data type of the year field to fix errors.
Sum up gdp to get world_gdp.
Group and order by year (in descending order).

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SELECT 
	year,
    -- Pull decade, decade_truncate, and the world's gdp
    DATE_PART(____) AS decade,
    DATE_TRUNC(____) AS decade_truncated,
    ____ AS world_gdp
FROM ____
-- Group and order by year in descending order
GROUP BY ____
ORDER BY ____;

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