复杂的 SQL Server 查询

Question

我正在尝试编写一个 SQL (Server) 查询，该查询将返回当天的所有事件，并且对于列 recurring= 1 的所有事件，我希望它在当天返回此事件举行并在活动后的 52 周内举行。

我的表格结构如下：

Event
{
    event_id (PK)
    title,
    description,
    event_start DATETIME,
    event_end DATETIME,
    group_id,
    recurring
}

Users
{
    UserID (PK)
    Username
}

Groups
{
    GroupID (PK)
    GroupName
}

Membership
{
    UserID (FK)
    GroupID (FK)
}

我目前的代码如下：

     var db = Database.Open("mPlan");
    string username = HttpContext.Current.Request.Cookies.Get("mpUsername").Value;
    var listOfGroups = db.Query("SELECT GroupID FROM Membership WHERE UserID = (SELECT UserID from Users WHERE Username = @0 )",  username);
    foreach(var groupID in listOfGroups)
        {
            int newGroupID = groupID.GroupID;
            var result = db.Query(
                @"SELECT e.event_id, e.title, e.description, e.event_start, e.event_end, e.group_id, e.recurring
                FROM   event e
                JOIN   Membership m ON m.GroupID = e.group_id
                WHERE  e.recurring = 0
                AND    m.GroupID = @0
                AND    e.event_start >= @1
                AND    e.event_end <= @2
                UNION ALL
                SELECT e.event_id, e.title, e.description, DATEADD(week, w.weeks, e.event_start), DATEADD(week, w.weeks, e.event_end), e.group_id, e.recurring
                FROM   event e
            JOIN   Membership m ON m.GroupID = e.group_id
            CROSS JOIN 
                ( SELECT  row_number() OVER (ORDER BY Object_ID) AS weeks
                FROM SYS.OBJECTS
                ) AS w
                WHERE  e.recurring = 1
                AND    m.GroupID = @3
                AND DATEADD(WEEK, w.Weeks, e.event_start) >= @4 
                AND DATEADD(WEEK, w.Weeks, e.event_end) <= @5", newGroupID, start, end, newGroupID, start, end
            );

这导致当查询存储在数据库中的事件的日期时，将返回该事件和 52 周的事件。当一个人在这一周后的一周查询该事件时，没有返回任何内容。

Answer 1

最简单的解决方案是更改以下 2 行

AND    e.event_start >= @4
AND    e.event_end <= @5"

到

AND    DATEADD(WEEK, w.Weeks, e.event_start) >= @4
AND    DATEADD(WEEK, w.Weeks, e.event_end) <= @5"

但是，我建议将所有这些 SQL 放入存储过程中，SQL-Server 将缓存执行计划，它会导致（稍微）更好的性能。

CREATE PROCEDURE dbo.GetEvents @UserName VARCHAR(50), @StartDate DATETIME, @EndDate DATETIME
AS
BEGIN
-- DEFINE A CTE TO GET ALL GROUPS ASSOCIATED WITH THE CURRENT USER
;WITH Groups AS 
(   SELECT  GroupID 
    FROM    Membership  m
            INNER JOIN Users u
                ON m.UserID = u.UserID
    WHERE   Username = @UserName
    GROUP BY GroupID
),
-- DEFINE A CTE TO GET ALL EVENTS FOR THE GROUPS DEFINED ABOVE
AllEvents AS
(   SELECT  e.*
    FROM    event e
            INNER JOIN Groups m 
                ON m.GroupID = e.group_id
    UNION ALL
    SELECT  e.event_id, e.title, e.description, DATEADD(WEEK, w.weeks, e.event_start), DATEADD(WEEK, w.weeks, e.event_end), e.group_id, e.recurring
    FROM    event e
            INNER JOIN Groups m 
                ON m.GroupID = e.group_id
            CROSS JOIN 
            (   SELECT  ROW_NUMBER() OVER (ORDER BY Object_ID) AS weeks
                FROM    SYS.OBJECTS
            ) AS w
    WHERE  e.recurring = 1
)   
-- GET ALL EVENTS WHERE THE EVENTS FALL IN THE PERIOD DEFINED
SELECT  *
FROM    AllEvents
WHERE   Event_Start >= @StartDate
AND     Event_End <= @EndDate

END

然后你可以用

调用它

var result = db.Query("EXEC dbo.GetEvents @0, @1, @2", username, start, end);

这消除了在后面的代码中迭代组的需要。如果这确实是一个要求，那么您可以修改存储过程以将 @GroupID 作为参数，并根据需要更改 select 语句/where 子句。

我假设知道Common Table Expressions。他们不需要使查询工作，在我看来，它们只是让事情变得更清晰。如果需要，我可以在没有它们的情况下重写它。

Answer 2

我会根据一些琐碎的 SQL 一次检查一个参数，只是为了将它们排除为可能的罪魁祸首。像这样的：

var result = db.Query("select r=cast(@0 as varchar(80))",username);
var result = db.Query("select r=cast(@0 as int)",newGroupID);
var result = db.Query("select r=cast(@0 as datetime)",start);
var result = db.Query("select r=cast(@0 as datetime)",end);