use billing;

insert into contract_balances (
  contract_id, cash_balance, cash_balance_interval, 
  free_time_balance, free_time_balance_interval, 
  start, end) 
  select * from (
    select '1' as c1, '0' as c2, '0' as c3, '0' as c4, '0' as c5, '2014-01-01 00:00:00', '2014-01-31 23:59:59'
  ) as tmp where not exists (select id from contract_balances where contract_id = 1) limit 1;