联合查询在前面的例子中已经出现过,只不过没有细说。

先来个例子吧

DbSession.Default.From<Customers>()
                .InnerJoin<Orders>(Customers._.CustomerID == Orders._.CustomerID)
                .ToDataTable();

生成的sql

Text: 
SELECT * FROM [Customers] INNER JOIN [Orders] ON ([Customers].[CustomerID] = [Orders].[CustomerID])

是非常简单操作就完成了。

 

方法 联合查询(sql)
InnerJoin inner join
LeftJoin left join
RightJoin right join
CrossJoin cross join
FullJoin full join
Union union
UnionAll union all

 

还是上例子清爽一些

DbSession.Default.From<Customers>()
                .LeftJoin<Orders>(Customers._.CustomerID == Orders._.CustomerID)
                .Where(Customers._.Country == "USA")
                .ToDataTable();

生成的sql

Text: 
SELECT * FROM [Customers]
LEFT OUTER JOIN [Orders]
ON ([Customers].[CustomerID] = [Orders].[CustomerID])
WHERE [Customers].[Country] = @e3c66f9aa65c498abfd76908621b567a

Parameters:
@e3c66f9aa65c498abfd76908621b567a[String] = USA

InnerJoin、LeftJoin、RightJoin、CrossJoin、FullJoin这个操作都是类似的。

三个表及以上关联例如

DbSession.Default.From<Customers>()
                .InnerJoin<Orders>(Customers._.CustomerID == Orders._.CustomerID)
                .InnerJoin<Order_Details>(Order_Details._.OrderID == Orders._.OrderID)
                .Where(Customers._.Country == "USA")
                .ToDataTable();
生成的sql:
Text: 
SELECT * FROM [Customers]
INNER JOIN [Orders] ON ([Customers].[CustomerID] = [Orders].[CustomerID])
INNER JOIN [Order Details] ON ([Order Details].[OrderID] = [Orders].[OrderID])
WHERE [Customers].[Country] = @5901349776db425492724e16c3c03a7a

Parameters:
@5901349776db425492724e16c3c03a7a[String] = USA

关联查询一下变简单了吧。

 

下面讲union 和 union all

这两个是两个结果的合集,union会区分结果排除相同的,union all 则直接合并结果集合。

DbSession.Default.From<Customers>().Where(Customers._.Country == "USA")
                .UnionAll(DbSession.Default.From<Customers>().Where(Customers._.Country == "UK"))
                .ToList();

生成的sql如下

Text: 
SELECT * FROM
(( SELECT * FROM [Customers] WHERE [Customers].[Country] = @f5b865bb20b64387b2c1be466c6d0980)
UNION ALL
( SELECT * FROM [Customers] WHERE [Customers].[Country] = @b7de905de065418dab5820094c764e1b))
AS Customers

Parameters:
@f5b865bb20b64387b2c1be466c6d0980[String] = USA @b7de905de065418dab5820094c764e1b[String] = UK

写到这里的时候发现了一个bug,所以请大家重新下载新版本。
 
union 和 union all用法是一样的,就不再举例子了。
 
 
下一节将讲述排序和分组。
posted on 2010-01-27 11:37  steven hu  阅读(3885)  评论(11编辑  收藏