SQL-每列的where条件

这是一个一般的SQL问题，但如果您一定要知道数据库是Firebird，我会告诉您

我有这张表（简化）：

基本上，我希望在结果上有多个字段，这些字段基于一个字段的总和（在本例中为数量），但基于不同的条件（在本例中为类型）

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提前感谢您的建议。

我不确定Firebird是如何做到的，但您能做一些类似的事情吗：

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

我正在引用PostgreSQL中我认为应该使用的内容，以防帮助您找到所需内容。

尝试以下方法：

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)

标准SQL是：

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"

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+1，尽管您需要引用

“user”

（并匹配列声明的大小写）。USER是当前_USER的Firebird同义词，它在您当前编写的查询中没有给出所需的结果。：）@皮尔克罗：你当然是对的，但这不只是一个模板吗？如果您认为此查询应该立即可运行，那么您应该提到

表

也必须被引用：@安德烈-嘿，疯狂的事情可能会发生，人们可以使用保留词，我也可以修复它，使它可以作为一个真正的查询运行。我想

type

没有被保留吗？@Damien：根据我的说法，似乎没有。（更新。但它被认为是一个关键词。）@Andriy，没错。然而，

user

并不像

table

那样到处都是保留字（至少MySQL和SQLite），在我看来，它似乎是原始帖子中使用的实际列名。谢谢

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)

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"