NQL.NET 数据库对象查询语言简介 2

      17. 比DataSet更简单的分页操作，并且性能也大大增强了，CurrentPageIndex = 1,PageSize = 5

this.dataGrid1.DataSource = new Query("Customers")
                .Where(Ex.Like("ContactTitle","Sales%"))
                .GetDataTable(1,5);

SQL  输出

SELECT TOP 5 *  FROM ( SELECT  * 
FROM Customers 
WHERE [ContactTitle]  LIKE @ContactTitle ) AS TMP 
WHERE TMP.CustomerID > (SELECT MAX(TMP3.CustomerID) FROM ( SELECT TOP 5 TMP2.CustomerID FROM ( SELECT  * 
FROM Customers 
WHERE [ContactTitle]  LIKE @ContactTitle ) AS TMP2 ORDER BY TMP2.CustomerID ASC) AS TMP3) ORDER BY TMP.CustomerID ASC

18。在计算列上可以进行+,-,*,/,%,++,--操作，在条件表达式上不仅可以进行算术运算而且可以进行逻辑运算 &&,||,! 以及进行比较运算==,!=,>,>=,<,<=,还可以进行范围运算%,in,between等运算

18.1 算术运算和比较运算

Query q = new Query("Products");
 Condition con = q.NewCondition("UnitPrice") * q.NewCondition("UnitsInStock") <=1000;
 this.dataGrid1.DataSource = con.GetDataTable();

SQL  输出

SELECT  * 
FROM Products 
WHERE 
    [UnitPrice] * [UnitsInStock] <= @UnitPrice

18.2 逻辑and 和范围Between

Query q = new Query("Products");
 ICondition con = q.NewCondition("UnitPrice") * q.NewCondition("UnitsInStock") <= 1000 
                && q.NewCondition("SupplierID").Between(1,5);
this.dataGrid1.DataSource = con.GetDataTable();

SQL  输出

SELECT  * 
FROM Products 
WHERE 
    [UnitPrice] * [UnitsInStock] <= @UnitPrice
    AND [SupplierID] BETWEEN @SupplierID AND @_Another_SupplierID

18.3 模糊查询%

Query q = new Query("Customers");
 this.dataGrid1.DataSource = q.Where(q.NewCondition("ContactTitle") % "Sales%").GetDataTable();

SQL  输出

SELECT  * 
FROM Customers 
WHERE 
    [ContactTitle] LIKE @ContactTitle

18.4 范围运算IN

Query qryCustomer = new Query("Customers")
                ._("CustomerID")
                .Where("ContactTitle","Owner");

Query qryOrder = new Query("Orders");
qryOrder.Where(    qryOrder.NewCondition("ShipVia") == 1 && qryOrder.NewCondition("CustomerID").In(qryCustomer));
 this.dataGrid1.DataSource = qryOrder.GetDataTable();

SQL  输出

SELECT  * 
FROM Orders 
WHERE 
    [ShipVia] = @ShipVia
    AND [CustomerID] IN (SELECT 
                                                        [CustomerID]
                             FROM Customers 
                             WHERE [ContactTitle]  = @ContactTitle )

18.5 复杂一点的条件

Query q = new Query("Products");
 Condition con = q.NewCondition("UnitPrice") >= 50 
                && (

                            q.NewCondition("UnitsInStock ") <= 20 
                          || q.NewCondition("UnitsOnOrder") > 0

                            )
                && q.NewCondition("ProductID") >6;

this.dataGrid1.DataSource = q.Where(con).GetDataTable();

SQL  输出

SELECT  * 
FROM Products 
WHERE 
    [UnitPrice] >= @UnitPrice
    AND (
        [UnitsInStock ] <= @UnitsInStock  OR [UnitsOnOrder] > @UnitsOnOrder
    ) 
    AND [ProductID] > @ProductID

19 . 查询表达式另一种写法 算术运算 Add(+),Minus(-),Multiply(*),Divide(/),Mode (%),逻辑运算and,or,not

比较运算GreatThan(>,GT),GreaterEquals(>=,GE),Equal(==,EQ),LessEquals(<=,LE),Little(<,LT),NotEquals(!=,NE)

IsNull,IsNotNull,IgnoreCase(忽略大小写）等运算

Query q = new Query("Products");
Condition con = q.NewCondition("UnitPrice").GreaterEquals(50)
                .And

                  (
                         q.NewCondition("UnitsInStock ").LessEquals(20)
                         .Or

                              (
                                  q.NewCondition("UnitsOnOrder").GreaterThan(0)

                              )
                )
                .And(q.NewCondition("ProductID").GT(6));
            this.dataGrid1.DataSource = q.Where(con).GetDataTable();

SQL  输出

SELECT  * 
FROM Products 
WHERE 
    [UnitPrice] >= @UnitPrice
    AND (
        [UnitsInStock ] <= @UnitsInStock  OR [UnitsOnOrder] > @UnitsOnOrder
    ) 
    AND [ProductID] > @ProductID

20. Case When 语句的用法

Query q = new Query("Orders");
 this.dataGrid1.DataSource = q.Select("OrderID",

                      "ShipCountry",
                    q.Case("ShipCountry")
                        .When("France").Then("fc")
                        .When("USA").Then("us")
                        .When("German").Then("gm")
                        .Else("com")
                        .End().As("SC"),
                    "OrderDate")
                .GetDataTable();

SQL  输出

SELECT 
    [OrderID],
    [ShipCountry],
    CASE [ShipCountry]
        WHEN 'France' THEN 'fc'
        WHEN 'USA' THEN 'us'
        WHEN 'German' THEN 'gm'
        ELSE 'com'
        END AS SC,
    [OrderDate]
FROM Orders 

21 统计函数(Count,Avg,Max,Min,Sum)的用法

21.1 Count

Query q = new Query("Products").Count("ProductID");
            Condition con = q.NewCondition("UnitPrice") * q.NewCondition("UnitsInStock") <=1000;
            this.richTextBox1.Text = con.GetScalar().ToString();

SQL  输出

SELECT 
    COUNT([Products].[ProductID])
FROM Products 
WHERE 
    [UnitPrice] * [UnitsInStock] <= @UnitPrice

21.2 Avg,其它的Max,Min,Sum用法一样

Query q = new Query("Products").Avg("ProductID");
            Condition con = q.NewCondition("UnitPrice") * q.NewCondition("UnitsInStock") <=1000;
            this.richTextBox1.Text = con.GetScalar().ToString();

SQL 输出

SELECT 
    AVG([Products].[ProductID])
FROM Products 
WHERE 
    [UnitPrice] * [UnitsInStock] <= @UnitPrice

22 GroupBy的用法

Query q = new Query("Orders")
                .Select("ShipVia","ShipRegion")
                .GroupBy("ShipVia","ShipRegion");
            this.dataGrid1.DataSource = q.GetDataTable();

SQL  输出

SELECT 
    [ShipVia],
    [ShipRegion]
FROM Orders 
 GROUP BY ShipVia,ShipRegion

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