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This article to share with you is about SQL Server database how to achieve nested subqueries, Xiaobian feel quite practical, so share to everyone to learn, I hope you can read this article after harvest, not much to say, follow Xiaobian to see it.

How to Use SQL Server Database Nested Subqueries

There are two subquery types: standard and related. The standard subquery is executed once and the results are fed back to the parent query. Related child queries are executed once per line and retrieved by the parent query. In this article, I'll focus on nested subqueries (I'll cover related subqueries later).

Consider this problem: You want to generate a list of salespeople who sell flat washers. The data you need is spread out in four tables: Personnel. Person.Contact, Human Resources. Employee (HumanResources.Employee), Sales. Sales.SalesOrderHeader, Sales. Sales.SalesOrderDetail. In SQL Server, you write programs from the outside-in, but it is helpful to start thinking from the inside-out, i.e., one statement that solves the need at a time.

If you write from the inside out, you can check the Sales.SalesOrderDetail table to match the ProductNumber value in the LIKE statement. You concatenate these rows with the Sales.SalesOrderHeader table, from which you get SalesPersonIDs. Then use SalesPersonID to join the SalesPersonID table. Finally, join the Person.Contact table using the ContactID.

USEAdventureWorks;

GO

SELECTDISTINCTc.LastName,c.FirstName

FROMPerson.ContactcJOINHumanResources.Employeee

ONe.ContactID=c.ContactIDWHEREEmployeeIDIN

(SELECTSalesPersonID

FROMSales.SalesOrderHeader

WHERESalesOrderIDIN

(SELECTSalesOrderID

FROMSales.SalesOrderDetail

WHEREProductIDIN

(SELECTProductID

FROMProduction.Productp

WHEREProductNumberLIKE"FW%")));

GO

How to Use SQL Server Database Nested Subqueries

This example reveals several wonderful things about SQL Server. As you can see, you can replace SELECT statements with IN() arguments. In this case, there are two applications, thus creating a nested subquery.

I am a fan of normalization, although I do not accept its absurd length. Complexity is increased because standardization has various queries. Subqueries are useful in these situations, and nested subqueries are even more useful.

The above is how to implement nested subqueries in SQL Server database. Xiaobian believes that some knowledge points may be seen or used in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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