Beginning SQL How do I sum and pick columns in the same line? -

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i started learning sql on w3schools.com today, , want make sure i'm on right track.

i'm trying solve problem:

write sql statement finding combined population of u.s. , mexico (in database).

i can't post table here because of lack of reputation, simple. given mexico's country id 2 , u.s. id 5.

the table has 4 columns, city_id, name, country_id, , population. not know how many rows there are. need add population columns have corresponding '2' or '5' country id.

this have far:

//this statement gives result-set cities in mexico , u.s. select * city country_id=’5’ or country_id=’2’  //here, don't know how reference result-set select sum(population) result-set

the question says in 1 statement, there simpler way this? thanks.

you put sum(population) expression query..

select sum(population) totalpopulation   city  country_id='5'     or country_id='2'

note can write x=a or x=b x in (a,b), i.e.

 country_id in (5,2)

(you can drop quotes if country_id integer although won't fail them)


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