一次计算具有多个条件的匹配行数的最有效方法

Question

我有一个非常大的表（称为 device_operation 有 5000 万行），其中包含产品在其生命周期中的所有操作（例如“开始”、“停止”、“重新填充”、...”和状态这些操作（行状态：已完成，失败），以及关联设备的 ID（行 device_id）和每个操作的时间戳（行 create_date）。

类似这样的：

/------+-----------+------------------+---------\
|   ID | Device ID | Create_Date      |  Status |
+------+-----------+------------------+---------+
|    1 |         1 | 2012-03-04 01:43 | Success |
|    2 |         4 | 2012-04-04 02:34 |  Failed |
|    3 |         9 | 2013-01-01 01:23 |  Failed |
|    4 |         4 | 2013-12-12 12:34 | Success |
|    5 |        23 | 2014-02-01 03:45 | Success |
|    6 |         1 | 2014-05-03 08:34 |  Failed |
\------+-----------+------------------+---------/

我还有另一个表（称为订阅），它告诉我产品的保修开始时间（行 create_date）（行 device_id）。保修期为一年。

/-----------+------------------\
| Device ID |      Create_Date |
+-----------+------------------+
|         2 | 2011-04-03 05:00 |
|         4 | 2012-03-05 03:45 |
|         5 | 2012-03-05 06:07 |
|       ... |              ... |
\-----------+------------------/

我正在使用 PostgreSQL。

我想做以下事情：

• 列出在给定日期 (2014-07-06) 之前至少有一次成功操作的所有设备 ID

对于这些设备中的每一个，计数：

• 在该日期 + 2 天 (2014-07-08) 之后的失败操作次数，并且尝试操作时设备在保修期内
• 在该日期 + 2 天 (2014-07-08) 之后的失败操作次数，并且在尝试操作时设备不在保修范围内
• 该日期之后成功操作的次数（设备是否在保修期内）

我在以下方面取得了一些有限的成功（为了便于阅读，查询已被稍微简化 - 还涉及到其他连接以获取订阅表，以及将设备包含在列表中的其他条件）：

SELECT distinct device_operation.device_id as did, subscription.create_date,
(
    SELECT COUNT(*)
    FROM device_operation dop
    WHERE dop.device_id = device_operation.device_id and
    dop.create_date > '2014-07-08' and
    dop.status = 'Success'
) as success,
(
    SELECT COUNT(*)
    FROM device_operation dop2
    WHERE
    dop2.device_id = subscription.device_id and
    dop2.create_date > '2014-07-08' and
    dop2.status = 'Failed' and
    dop2.create_date <= subscription.create_date + interval '1 year'
) as failed_during_warranty,
(
    SELECT COUNT(*)
    FROM device_operation dop2
    WHERE
    dop2.device_id = subscription.device_id and
    dop2.create_date > '2014-07-08' and
    dop2.status = 'Failed' and
    dop2.create_date > subscription.create_date + interval '1 year'
) as failed_after_warranty,
FROM device_operation, subscription
WHERE
device_operation.status = 'Success' and -- list operations which are successful
device_operation.create_date <= '2014-07-06' and -- list operations before that date
device_operation.device_id = subscription.device_id -- get warranty start for each operation
ORDER BY success DESC, failed_during_warranty DESC, failed_after_warranty DESC

您可以猜到，它太慢了，我无法运行查询。但是，它可以让您了解结构。

我尝试使用 NULLIF 将请求合并为一个，希望它能让 PostgreSQL 只列出一次子查询而不是 3 个，但它返回“子查询必须只返回一列”：

SELECT distinct device_operation.device_id as did, subscription.create_date,
(
SELECT COUNT(NULLIF(dop2.status != 'Success', true)) as completed, 
    COUNT(NULLIF(dop2.status != 'Failed' or not (dop2.create_date <= subscription.create_date + interval '1 year'), true)) as failed_in_warranty, 
    COUNT(NULLIF(dop2.status != 'Failed' or     (dop2.create_date <= subscription.create_date + interval '1 year'), true)) as failed_after_warranty
FROM device_operation dop2
WHERE
    dop2.device_id = device_operation.device_id and
    dop2.device_id = subscription.device_id and
    dop2.create_date > '2014-07-08'
) as subq
FROM device_operation, subscription
WHERE
device_operation.status = 'Success' and -- list operations which are successful
device_operation.create_date <= '2014-07-06' and -- list operations before that date
device_operation.device_id = subscription.device_id -- get warranty start for each operation
ORDER BY success DESC, failed_in_warranty DESC, failed_outside_warranty DESC

我也尝试将子查询移动到 FROM 子句，但这不起作用，因为我需要为主查询的每一行运行子查询（或者我是否？也许有更好的方法）

我期望的是这样的：

/-----------+---------+------------------------+-----------------------\
| Device ID | Success | Failed during warranty | Failed after warranty |
+-----------+---------+------------------------+-----------------------+
|    194853 |      10 |                      0 |                     0 |
|      7853 |       5 |                      5 |                     0 |
|      5848 |       3 |                      0 |                    56 |
|   8546455 |       0 |                     45 |                     0 |
|       102 |       0 |                      4 |                     1 |
|  69329548 |       0 |                      0 |                     9 |
|        17 |       0 |                      0 |                     0 |
\-----------+---------+------------------------+-----------------------+

有人可以帮我找到最有效的方法吗？

编辑：极端情况：您可以认为所有设备都有订阅条目。

非常感谢！

Answer 1

我认为您只需要条件聚合。我发现数据结构和逻辑有点难以理解，但我认为以下基本上是您需要的：

SELECT d.device_id,
       SUM(CASE WHEN d.status = 'Failed' AND d.create_date <= '2014-07-06' + interval '2 day'
                THEN 1 ELSE 0
           END) as NumFails,
       SUM(CASE WHEN d.status = 'Failed' AND d.create_date <= '2014-07-06' + interval '2 day' AND
                     d.create_date > s.create_date + interval '1 year'
                THEN 1 ELSE 0
           END) as NumFailsNoWarranty,
       SUM(CASE WHEN d.status = 'Success' AND d.create_date <= '2014-07-06' + interval '2 day'
                THEN 1 ELSE 0
           END) as NumSuccesses
FROM device_operation d JOIN
     subscription s
     ON d.device_id = s.device_id
GROUP BY d.device_id
HAVING SUM(CASE WHEN d.status = 'Success' AND d.create_date <= '2014-07-06' THEN 1 ELSE 0 END) > 0;