Question

我一直在使用Entity Framework和LINQ开发XML解析系统，现在我在翻译以前没有采用标准化格式的SQL查询时遇到了一些问题。

我有以下结构：

1. Message                     (Each message type has one to many messagetype341s)
2. MessageType341              (Each messagetype341 has 1 to many meters)       
3. Meter                       (Each meter has 2 channel informations)
4. ChannelInformation          (Each channel information has 48 interval informations)
5. Interval Information

ReadDate 和 CustomerNo 处于MessageType341级别。我正在尝试写续集，其中我将CustomerNo和ReadDate作为变量，然后根据列出的messagetype341s的返回，然后检索相关messagetype341s的后续计量表，通道信息和间隔信息

我尝试了以下内容：

SELECT c.SerialNumber,
       b.ReadDate,
       d.RegisterTypeCode,
       e.IntervalStatusCode,
       d.UOM_Code,
       e.IntervalPeriodTimestamp,
       e.IntervalValue
FROM   MarketMessage AS a,
       MessageType341 AS b,
       Meter AS c,
       ChannelInformation AS d,
       IntervalInformation AS e
WHERE  b.CustomerNo = '12348750528'
       AND b.ReadDate >= '01 nov 2014'
       AND b.ReadDate <= '30 nov 2014'
ORDER  BY b.ReadDate

但它似乎没有返回与我的预期值匹配的值，我是否采用了错误的方式？

Answer 1

根据我的理解，你需要使用LEFT jons。

select c.SerialNumber, b.ReadDate, d.RegisterTypeCode, e.IntervalStatusCode, d.UOM_Code,   e.IntervalPeriodTimestamp, e.IntervalValue
from MarketMessage as a LEFT JOIN MessageType341 as b ON a.PK = b.FK
LEFT JOIN  Meter as c ON b.PK = c.FK
LEFT JOIN  ChannelInformation as d ON c.PK = d.FK
LEFT JOIN  IntervalInformation as e ON d.PK = e.FK
where b.CustomerNo = '12348750528'
and b.ReadDate BETWEEN '01 nov 2014' AND and b.ReadDate <= '30 nov 2014'
order by b.ReadDate

其中：

PK =主键

FK =外键

每种类型的加入之间的差异，请参阅：Visual Representation of SQL Joins

Answer 2

您使用旧的JOIN语法，而不是过滤这些结果：

SELECT *
FROM Table1,Table2

返回Table1与Table2，CROSS JOIN或笛卡尔积的每一行配对的每一行。

您可以根据关系过滤结果，即：WHERE Table1.ID = Table2.Parent_ID，但最好使用标准JOIN语法：

SELECT c.SerialNumber, b.ReadDate, d.RegisterTypeCode, e.IntervalStatusCode, d.UOM_Code,   e.IntervalPeriodTimestamp, e.IntervalValue
FROM MarketMessage as a
JOIN MessageType341 as b
  ON a.ID = b.Parent_ID
JOIN Meter as c
  ON b.ID = c.Parent_ID
JOIN ChannelInformation as d
  ON c.ID = d.Parent_ID
JOIN IntervalInformation as e
  ON d.ID = e.Parent_ID
WHERE b.CustomerNo = '12348750528'
  AND b.ReadDate >= '01 nov 2014'
  AND b.ReadDate <= '30 nov 2014'
ORDER BY b.ReadDate

如果您有一些没有孩子的记录，您可以更改为LEFT JOIN以恢复所有记录，无论他们是否拥有各种级别的信息。

检索与变量匹配的父类的子实体列表

2 个答案: