Using the EXISTS Operator

Retrieving Data / Retrieving Duplicate Rows

SELECT a.*
FROM countrylanguage a
WHERE
    a.IsOfficial = 'T' AND
    EXISTS (
        SELECT 1
        FROM countrylanguage b
        WHERE
            b.CountryCode = a.CountryCode AND
            b.IsOfficial = a.IsOfficial AND
            b.`Language` <> a.`Language`
    )

CountryCode	Language	IsOfficial	Percentage
AFG	Pashto	T	52.4
AFG	Dari	T	32.1
ANT	Papiamento	T	86.2
ANT	Dutch	T	0.0
ASM	Samoan	T	90.6
ASM	English	T	3.1
BDI	Kirundi	T	98.1
BDI	French	T	0.0
BEL	French	T	32.6
BEL	German	T	1.0
...

The entries in the country language table are selected if the language is official and there is another official language in that country.
The EXISTS operator allows a subquery to be executed and returns true when the subquery returns one or more records.