3. (World database) All questions below are related to the following query Selec

Question

3. (World database) All questions below are related to the following query Select co.name as "Name", sum (ct.population) "Major City Population" From Country co Join City ct on (co.code ct.countrycode ) Where co.continent 'Europe' Group by co.name; a. Is column alias used? How? b. Is table alias used? How? c. Is join used? What are the tables? d. Is there a selection operation involved? e. Is there a projection operation involved? f. Is any aggregation function used? Which one? g. Is grouping used? How? h. What the output looks like (number of columns, headers, a sample row, etc.)? 4. (World database) A relational algebra expression is nuitr me i Cownry comtinen Northmerica (City Country)) where F is the expression Country.code statement for the algebra expression - City countrycode. Write a SQL select

Explanation / Answer

a. yes, column alias is used, in "co.name as Name".

b. yes, table alias is used, in FROM country co. co is alias for table couunty.

c. yes join is used on tables Country and City.

d. Yes, there is a selection operation WHERE co.continent = 'Europe' WHERE clause is selection

e. Yes there is a Projection operation SELECT clause is projection operation

f. yes, aggregate function sum() is used.

g. yes gouping is used due to GROUP BY clause.

h.

number of coulumns = 2.

Name-----Major City Population

India====20000

USA======50000

4. SELECT co.name as Country_Name, c.name as City_Name

FROM Country co JOIN City c

ON (co.code = x.countrycode)

WHERE co.continent = 'North America'

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