在 INNER JOIN SQL 查询上使用 GROUP BY 和 ORDER BY

Question

我正在使用以下查询从三个表中对客户的工作时间和费用进行分组，一张用于客户，一张用于工作时间，一张用于费用：

SELECT  a.*,
        COALESCE(b.totalCount, 0) AS CountWork,
        COALESCE(b.totalAmount, 0) AS WorkTotal,
        COALESCE(c.totalCount, 0) AS CountExpense,
        COALESCE(c.totalAmount, 0) AS ExpenseTotal
FROM    clients A
        LEFT JOIN
        (
            SELECT  Client, 
                    COUNT(*) totalCount,
                    SUM(Amount) totalAmount
            FROM    work_times
            WHERE   DATE BETWEEN '2013-01-01' AND '2013-02-01'
            GROUP   BY Client
        ) b ON a.Client = b.Client
        LEFT JOIN
        (
            SELECT  Client, 
                    COUNT(*) totalCount,
                    SUM(Amount) totalAmount
            FROM    expenses
            WHERE   DATE BETWEEN '2013-01-01' AND '2013-02-01'
            GROUP   BY Client
        ) c ON a.Client = c.Client
WHERE   b.Client IS NOT NULL OR
        c.Client IS NOT NULL

您可以看到查询在小提琴here 中工作。

我正在尝试修改此查询，以便每个客户每个月都有一行，按月排序，然后按客户排序。我正在尝试使用以下修改后的查询来做到这一点：

SELECT  a.*,
        COALESCE(b.totalCount, 0) AS CountWork,
        COALESCE(b.totalAmount, 0) AS WorkTotal,
        COALESCE(c.totalCount, 0) AS CountExpense,
        COALESCE(c.totalAmount, 0) AS ExpenseTotal
FROM    clients A
        LEFT JOIN
        (
            SELECT  Client, 
                    COUNT(*) totalCount,
                    SUM(Amount) totalAmount,
                    SUBSTR(Date, 1, 7) as Month
            FROM    work_times
            GROUP   BY Month,Client
            ORDER BY Month
        ) b ON a.Client = b.Client
        LEFT JOIN
        (
            SELECT  Client, 
                    COUNT(*) totalCount,
                    SUM(Amount) totalAmount,
                    SUBSTR(Date, 1, 7) as Month
            FROM    expenses
            GROUP   BY Month,Client
            ORDER BY Month,Client
        ) c ON a.Client = c.Client
WHERE   b.Client IS NOT NULL OR
        c.Client IS NOT NULL

您可以看到修改后的查询在运行here。

但它的工作并不完全正确。即使有 2013 年 1 月的工作时间和 2013 年 2 月的费用（因此应该有 2 行），客户 B 也只返回一行，并且看起来这些行是由客户而不是按月排序的。有人可以建议如何修改查询以获得所需的输出，对于第二个小提琴上的示例来说，它是：

╔════════╦═══════════╦═══════════╦══════════════╦══════════════╗
║ CLIENT ║ COUNTWORK ║ WORKTOTAL ║ COUNTEXPENSE ║ EXPENSETOTAL ║
╠════════╬═══════════╬═══════════╬══════════════╬══════════════╣
║ A      ║         1 ║        10 ║            1 ║           10 ║
║ B      ║         1 ║        20 ║            0 ║            0 ║
║ A      ║         1 ║        15 ║            0 ║            0 ║
║ B      ║         0 ║        0  ║            1 ║           10 ║
║ C      ║         1 ║        10 ║            0 ║            0 ║
╚════════╩═══════════╩═══════════╩══════════════╩══════════════╝

Answer 1

除非我在要求中遗漏了某些内容，否则您需要做的是获取客户列表和日期，然后将其加入您的子查询。所以您的查询将是：

SELECT a.*,
  COALESCE(b.totalCount, 0) AS CountWork,
  COALESCE(b.totalAmount, 0) AS WorkTotal,
  COALESCE(c.totalCount, 0) AS CountExpense,
  COALESCE(c.totalAmount, 0) AS ExpenseTotal
FROM 
(
  select distinct c.Client, d.Month
  from clients c
  cross join
  (
    select SUBSTR(Date, 1, 7) as Month
    from work_times
    union 
    select SUBSTR(Date, 1, 7) as Month
    from expenses
  ) d
) A
LEFT JOIN
(
  SELECT  Client, 
    COUNT(*) totalCount,
    SUM(Amount) totalAmount,
    SUBSTR(Date, 1, 7) as Month
  FROM    work_times
  GROUP   BY Month,Client
  ORDER BY Month,Client
) b 
  ON a.Client = b.Client
  and a.month = b.month
LEFT JOIN
(
  SELECT  Client, 
    COUNT(*) totalCount,
    SUM(Amount) totalAmount,
    SUBSTR(Date, 1, 7) as Month
  FROM    expenses
  GROUP   BY Month,Client
  ORDER BY Month,Client
) c 
  ON a.Client = c.Client
  and a.month = c.month
WHERE   b.Client IS NOT NULL OR
        c.Client IS NOT NULL
order by a.month, a.client

见SQL Fiddle with Demo。

结果是：

| CLIENT |   MONTH | COUNTWORK | WORKTOTAL | COUNTEXPENSE | EXPENSETOTAL |
--------------------------------------------------------------------------
|      A | 2013-01 |         1 |        10 |            1 |           10 |
|      B | 2013-01 |         1 |        20 |            0 |            0 |
|      A | 2013-02 |         1 |        15 |            0 |            0 |
|      B | 2013-02 |         0 |         0 |            1 |           20 |
|      C | 2013-02 |         1 |        10 |            0 |            0 |

Answer 2

如果您在子查询中进行排序，则没关系，因为外部查询可能（并且可能需要）重新排序结果。您想在外部查询中添加 order by。

您的问题是您尝试按 B 表的月份和客户进行排序，并且还尝试按 C 表的月份和客户进行排序。需要定义B.month、B.client、C.month的顺序，并放入order by进行外层查询。

顺便说一句，如果你只在 C 表的子查询中按月分组，那么客户端是没有意义的。某些数据库（如 DB2）不允许您将未聚合的字段放在 select 中，如果它不在 group by 中。