SQL-每列的条件。

SELECT \"user\",
    SUM(CASE WHEN type=\'credit\' then amount END) as Credit,
    SUM(CASE WHEN type=\'debit\' then amount END) as Debit
FROM
    \"table\"
GROUP BY
    \"user\"

SELECT user, 
sum(SELECT amount FROM table AS t2 WHERE t2.user = t1.user AND type=\"credit\" ) AS credit, 
sum(SELECT amount FROM table AS t3 WHERE t3.user = t1.user AND type=\"debit\" ) AS debit
FROM table AS t1
GROUP BY user
ORDER BY user

SELECT credit.user_name, credit.cre, debit.deb
  FROM (SELECT user_name, SUM(amount) cre FROM t WHERE TYPE = \'credit\' GROUP BY user_name) credit
  LEFT OUTER JOIN (SELECT user_name, SUM(amount) deb
                     FROM t
                    WHERE TYPE = \'debit\'
                    GROUP BY user_name) debit
    ON (credit.user_name = debit.user_name)