common_query.rb

# Under STI, find the top 10 accounts with the greatest balances
# with just one query.

top_accounts = Account.order(balance: :desc).limit(10)

# Under MTI, we need to query all accounts and sort them in memory:

top_corporate_accts =  CorporateAccount.order(balance: :desc).limit(10)
top_sb_accts =  SmallBusinessAccount.order(balance: :desc).limit(10)
top_personal_accts =  PersonalAccount.order(balance: :desc).limit(10)

top_accounts = (top_corporate_accts + top_sb_accts + top_personal_accts).sort do |acct1, acct2|
  acct1 <=> acct2
end.first(10)