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326378 2010 年 12 月 09 日 14:31 Reading (loading. ..) Comments (1) Category: SQL database
There are two types of sub-query: standards and relevant. Standard sub-query execution time, the results fed back to the parent query. Correlated subquery once for each row, retrieve the parent query. In this article, I will focus on the nested subqueries (nested subqueries) (I will later introduce the relevant sub-query).
Consider this question: Do you want to generate a sales staff to sell a list of flat washers. You need a table of data scattered in four categories: personnel. Contact (Person.Contact), human resources. Staff (HumanResources.Employee), sales. Sales Order title (Sales.SalesOrderHeader), sales. Sales Order Details (Sales. SalesOrderDetail). In SQL Server, you from the internal pressure (outside-in) write a program,
tory burch outlet, but external pressure type (inside-out) began to consider very helpful, which can be a solution needs a statement.
If you write from the inside out, the can check Sales.SalesOrderDetail form matching products in the LIKE statement number (ProductNumber) value. You will connect these lines with the Sales.SalesOrderHeader form,
tory burch wedge, can be obtained from sales staff IDs (SalesPersonIDs). SalesPersonID SalesPersonID connection and then use the form. Finally, ContactID connection Person.Contact form.
USE AdventureWorks;
GO
SELECT DISTINCT c.LastName,
tory burch flip flops sale, c.FirstName
FROM Person.Contact c JOIN HumanResources.Employee e
ON e.ContactID = c.ContactID WHERE EmployeeID IN
(SELECT SalesPersonID
FROM Sales.SalesOrderHeader
WHERE SalesOrderID IN
(SELECT SalesOrderID
FROM Sales.SalesOrderDetail
WHERE ProductID IN
(SELECT ProductID
FROM Production. Product p
WHERE ProductNumber LIKE'FW %')));
GO
This example reveals about the SQL Server a few wonderful things. You can find,
tory burch flip flops, you can use IN () parameter substitution SELECT statement. In this case, there are two applications,
tory burch shoes, thus creating a nested sub-queries.
I standardized (normalization) of the fans, although I do not accept the absurd length. As standard with a variety of inquiries increased complexity. Erupted in these cases it is very useful for queries, nested subqueries even more useful.
problem when you need when dispersed in many forms, you have them together again, then you may find very useful for nested subroutine.