如何从SQL中的表中的列获取最新日期？

Question

我正在尝试使用sql，asp.net从OrderItem表中获取最新日期。 但是，当我运行程序时，它们显示此错误： Incorrect syntax near the keyword 'from'.

这是我的代码：

    string strconnect =  ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
    SqlConnection myConnect = new SqlConnection(strconnect);

    string command = "
      Select OrderItem.ProductID, Product.Name, OrderItem.TotalQty, Product.UnitPrice, OrderItem.TotalPrice 
      FROM OrderItem 
      INNER JOIN Product ON OrderItem.ProductID=Product.ProductID 
      WHERE OrderDate = MAX(OrderDate) from OrderItem";
    SqlCommand cmd = new SqlCommand(command, myConnect);

    myConnect.Open();

    SqlDataReader reader = cmd.ExecuteReader();

    GridView1.DataSource = reader;
    GridView1.DataBind();
    reader.Close();
    myConnect.Close();

请指教！

Answer 1

由于已在FROM子句中指定，因此需要在WHERE条件中删除“ from OrderItem”。

SELECT
    i.ProductID,
    p.Name,
    i.TotalQty,
    p.UnitPrice,
    i.TotalPrice 
FROM 
    OrderItem i
        INNER JOIN Product p
            ON i.ProductID = p.ProductID 
WHERE
    i.OrderDate = (SELECT MAX(OrderDate) 
                   FROM OrderItem 
                   WHERE OrderItem.ProductID = i.ProductID)

Answer 2

SELECT o.ProductID, p.Name, o.TotalQty, p.UnitPrice, o.TotalPrice 
FROM OrderItem AS o
INNER JOIN Product AS p ON o.ProductID = p.ProductID
ORDER BY o.OrderDate DESC
LIMIT 1

啊，您正在使用SQL服务器，请尝试以下操作：（但未经测试）

SELECT TOP 1 o.ProductID, p.Name, o.TotalQty, p.UnitPrice, o.TotalPrice 
FROM OrderItem AS o
INNER JOIN Product AS p ON o.ProductID = p.ProductID
ORDER BY o.OrderDate DESC

Answer 3

这取决于订购日期的数据类型。 您可能需要更改变量的数据类型或应用截断。

declare @MaxOrderDate datetime
select @MaxOrderDate = MAX(OrderItem.OrderDate) from OrderItem

Select
    OrderItem.ProductID,
    Product.Name,
    OrderItem.TotalQty,
    Product.UnitPrice,
    OrderItem.TotalPrice 
FROM 
    OrderItem 
        INNER JOIN Product 
            ON OrderItem.ProductID=Product.ProductID 
WHERE
    OrderItem.OrderDate = @MaxOrderDate

Answer 4

您应该在WHERE子句中更改子查询。

SELECT OrderItem.ProductID, Product.Name, OrderItem.TotalQty, Product.UnitPrice, OrderItem.TotalPrice 
FROM OrderItem 
INNER JOIN Product ON OrderItem.ProductID=Product.ProductID 
WHERE OrderDate = ( SELECT MAX(OrderDate) FROM OrderItem );