Question

I’m trying to learn sql and I get this error – what does it mean?.

I’m trying to : Get countries that have a GDP greater than any country in Europe?

Error:

[Microsoft][ODBC SQL Server Driver][SQL Server]Subquery returned more
than 1 value. This is not permitted when the subquery follows =, !=,
<, <= , >, >= or when the subquery is used as an expression.
(SQL-21000)

select name, gdp from bbc 
where gdp > 
(
    select gdp from bbc
    where region = 'Europe'
)

Answer 1

The message describes the error adequately: your table has many countries in Europe, so > operator cannot be applied without some aggregation or more constraints in the subquery:

select name, gdp from bbc 

where gdp > 

(
select max(gdp) from bbc
where region = 'Europe'

)

Adding max ensures that there would be precisely one number selected, and that number is the highest GDP among all European countries¹.

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¹ You might as well select the GDP of Germany right away 🙂