Question

我在Postgresql中有两个表，如下所示：

收据

id CHARACTER VARYING(20),
account CHARACTER VARYING(20),
date DATE,
amount NUMERIC(8,2),
PRIMARY KEY(id)

non_cash

id CHARACTER VARYING(20),
account CHARACTER VARYING(20),
date DATE,
amount NUMERIC(8,2),
PRIMARY KEY(id)

现在，我想从SUM(amount)的两个表中account = '00210_pre'和SUM(amount)以及MAX(date)两个表格中选择account = '00210_int'。我可以使用2个查询获得所需的结果：

SELECT SUM(amount) AS int_total, MAX(date)
FROM (SELECT amount, date, account FROM non_cash
UNION SELECT amount, date, account FROM receipts) AS v
WHERE account = '00210_int'

和

SELECT SUM(amount) AS pre_total
FROM (SELECT amount, account FROM non_cash
UNION SELECT amount, account FROM receipts) AS v
WHERE account = '00210_pre'

现在我的问题是是否可以在一个查询中使用上述内容？如果是，如何？

请注意，该帐户的后缀仅在 _pre 和 _int 中有所不同，其余数字相同。

Answer 1

您不应该使用UNION。您应该使用UNION ALL，因为UNION会删除重复项，这可能是不可取的，并且是浪费精力。但是，您的问题的答案是GROUP BY：

SELECT account, SUM(amount) AS int_total, MAX(date)
FROM ((SELECT amount, date, account FROM non_cash
      ) UNION ALL
      (SELECT amount, date, account FROM receipts)
     ) v
WHERE account IN ('00210_int', '00210_pre')
GROUP BY account;

注意：如果要组合值，请不要使用GROUP BY：

SELECT SUM(amount) AS int_total, MAX(date)
FROM ((SELECT amount, date, account FROM non_cash
      ) UNION ALL
      (SELECT amount, date, account FROM receipts)
     ) v
WHERE account IN ('00210_int', '00210_pre');

编辑：

要获得单行使用条件聚合：

SELECT SUM(CASE WHEN account = '00210_int' THEN amount ELSE 0 END) AS int_total,
       SUM(CASE WHEN account = '00210_pre' THEN amount ELSE 0 END) AS pre_total,
       MAX(date)
FROM ((SELECT amount, date, account FROM non_cash
      ) UNION ALL
      (SELECT amount, date, account FROM receipts)
     ) v
WHERE account IN ('00210_int', '00210_pre');

Answer 2

SELECT left(nc.account,5) account, 
    max(greatest(nc.date, r.date)) max_date,
    sum(nc.amount + r.amount) total
    sum(CASE WHEN nc.account = '00210_int' OR r.account = '00210_int' THEN 
            nc.amount + r.amount
            ELSE NULL
            END
            ) int_total,
    sum(CASE WHEN nc.account = '00210_pre' OR r.account = '00210_pre' THEN 
            nc.amount + r.amount
            ELSE NULL
            END
            ) pre_total
FROM non_cash nc
INNER JOIN receipts r
ON left(nc.account,5) = left(r.account,5)
WHERE nc.account  IN ( '00210_int', '00210_pre')
OR r.account  IN ( '00210_int', '00210_pre')
GROUP BY 1

对于下面提到的案例，是否可以有1个查询而不是2个查询？

2 个答案: