基于条件的T-SQL强制空值

这是我的看法

 SELECT e.Text AS StatusText,
        a.Created AS [DATE],
        a.Username,
        b.Name AS CustomerName,
        c.Name AS ServiceName,
        d.Message AS DeviationMessage
   FROM dbo.StatusUpdate AS a
        LEFT OUTER JOIN dbo.Customer AS b ON a.CustomerId = b.CustomerID
        LEFT OUTER JOIN dbo.Service AS c ON a.ServiceId = c.ServiceID
        LEFT OUTER JOIN dbo.Deviation AS d ON a.DeviationId = d.DeviationID
        LEFT OUTER JOIN dbo.StatusText AS e ON a.Status = e.ID

我想做的是：当a.Status（int）为2或3时，我想强制a.Username显示为NULL。我应该如何处理这个问题？

试试这个：

 SELECT e.Text AS StatusText,
        a.Created AS [DATE],
        CASE a.status
            WHEN 2 THEN NULL
            WHEN 3 THEN NULL
            ELSE a.Username
        END,  
        b.Name  AS CustomerName,
        c.Name  AS ServiceName,
        d.Message AS DeviationMessage
   FROM dbo.StatusUpdate AS a
        LEFT OUTER JOIN dbo.Customer AS b ON a.CustomerId = b.CustomerID
        LEFT OUTER JOIN dbo.Service AS c ON a.ServiceId = c.ServiceID
        LEFT OUTER JOIN dbo.Deviation AS d ON a.DeviationId = d.DeviationID
        LEFT OUTER JOIN dbo.StatusText AS e ON a.Status = e.ID

试试这个：

 SELECT e.Text AS StatusText,
        a.Created AS [DATE],
        CASE a.status
            WHEN 2 THEN NULL
            WHEN 3 THEN NULL
            ELSE a.Username
        END,  
        b.Name  AS CustomerName,
        c.Name  AS ServiceName,
        d.Message AS DeviationMessage
   FROM dbo.StatusUpdate AS a
        LEFT OUTER JOIN dbo.Customer AS b ON a.CustomerId = b.CustomerID
        LEFT OUTER JOIN dbo.Service AS c ON a.ServiceId = c.ServiceID
        LEFT OUTER JOIN dbo.Deviation AS d ON a.DeviationId = d.DeviationID
        LEFT OUTER JOIN dbo.StatusText AS e ON a.Status = e.ID

---

通过案例陈述，你可以很容易地做到这一点

大概是

CASE WHEN Status = 3 THEN USERNAME IS NULL

---

这是未经测试的，但想法是存在的。

您可以通过案例陈述轻松实现这一点

大概是

CASE WHEN Status = 3 THEN USERNAME IS NULL

这是未经测试，但想法是存在的