CREATE TABLE contracts (
      code TEXT NOT NULL default '' COLLATE NOCASE,
      first_name TEXT NOT NULL default '' COLLATE NOCASE,
      last_name TEXT NOT NULL default '' COLLATE NOCASE
);

CREATE TABLE periods (
      contract_id INT NOT NULL default '0', 
      date_from REAL NOT NULL default '0.00', 
      date_to REAL NOT NULL default '0.00', 
      amount REAL NOT NULL default '0.00'
);

CREATE TABLE payments (
      contract_id INT NOT NULL default '0', 
      amount REAL NOT NULL default '0.00'
);

SELECT 
    t1.rowid, 
    t1.code, 
    t1.first_name, 
    t1.last_name, 
    MIN(t2.date_from) AS min_date, 
    MAX(t2.date_to) AS max_date,
    SUM(t2.amount) AS sum_amount,  
    (SELECT SUM(amount) AS sum_payment FROM payments AS t3 WHERE t3.contract_id = t1.rowid) 
FROM
    contracts AS t1 
LEFT OUTER JOIN 
    periods AS t2 
ON 
    t1.rowid = t2.contract_id 
GROUP BY 
    t1.rowid;