聯合查詢在前面的例子中已經出現過,只不過沒有細說。
先來個例子吧
DbSession.Default.From<Customers>() .InnerJoin<Orders>(Customers._.CustomerID == Orders._.CustomerID) .ToDataTable();
Text:
SELECT * FROM [Customers] INNER JOIN [Orders] ON ([Customers].[CustomerID] = [Orders].[CustomerID])
是非常簡單操作就完成了。
方法 | 聯合查詢(sql) |
InnerJoin | inner join |
LeftJoin | left join |
RightJoin | right join |
CrossJoin | cross join |
FullJoin | full join |
Union | union |
UnionAll | union all |
還是上例子清爽一些
DbSession.Default.From<Customers>() .LeftJoin<Orders>(Customers._.CustomerID == Orders._.CustomerID) .Where(Customers._.Country == "USA") .ToDataTable();
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這個操作都是類似的。
三個表及以上關聯例如
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
關聯查詢一下變簡單了吧。
下面講union 和 union all
這兩個是兩個結果的合集,union會區分結果排除相同的,union all 則直接合並結果集合。
DbSession.Default.From<Customers>().Where(Customers._.Country == "USA") .UnionAll(DbSession.Default.From<Customers>().Where(Customers._.Country == "UK")) .ToList();
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