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Answer 1

Question 1

Ans - Table name - enrollments

Here you have to return the sum of hours from the table. In SQL there is a function SUM( ) that user to give you sum of particular column.

SELECT SUM (hours) FROM enrollments WHERE class='Math';

This query will return the sum of hours where class is equal to Math.

Question 2

Ans - Table name - enrollments

Here you have to select only that rows that consist class name Biology so for that

SELECT * FROM enrollments WHERE class = 'Biology'

This will return all rows containing class name ' Biology'

Question 3

Ans- Table name - enrollments

Here you have to do same thing as question 2 but you have to select school must be equal to 'Math and Science'

SELECT * FROM enrollments WHERE class = 'Biology' AND school = 'Math and Science'

It will return all that matching rows.

Question 4

Ans - Table name - weather_station and weather_stats

Here you have to join to tables

SELECT * FROM weather_station INNER JOIN weather_stats ON weather_station.id = weather_stats.id;

Here you can use JOIN or INNER JOIN both are same.

Question 5

Ans - Table name - gold_prices

Here you have to calculate average for that there is a function AVG(), you can use that

SELECT AVG(price) FROM gold_prices

GROUP BY month, year

ORDER BY year

This will return your desired result

Question 6

Ans- Table name - weather_stats and weather_station

In this table you have to use Left join or right join as well but it depends to whom you are going to accordingly

SELECT * FROM weather_stats LEFT JOIN weather_station ON weather_stats.id = weather_station.id WHERE weather_stats.month = 1 OR weather_stats.month = 4