None of the examples you've given are valid for storing the results of a SQL select query - because none of them perform an SQL query but simply save a string in a variable (this is akin to writing "REALLY FAST CAR" on a piece of paper and then expecting that paper to win the Gran Prix.) As has been pointed out, you need to use a mechanism - e.g., the DB client directly, or the DBI module - which will perform that query. Here's an example of what that might look like:

# Silly example, but fits the spec
my @languages = qx#echo "select Language from CountryLanguage where Co
+untryCode='RUS'"|mysql -u username database_name#;
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Another example, more in line with how it would usually be coded:

#!/usr/bin/perl -w
use strict;
use DBI;
$|++;

my %info = (
    db      =>  "database_name",
    user    =>  "username",
    pass    =>  "pAsSwOrD"
);

my $dbh = DBI->connect("DBI:mysql:$info{db}", $info{user}, $info{pass}
+);
my $ref = $dbh->selectall_arrayref("select Language from CountryLangua
+ge where CountryCode='RUS'")
    or die $DBI::errstr;

my @languages = map { $_->[0] } @$ref;    # Store the first element ('
+Language') in array
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