使用：EXISTS (Transact-SQL)

指定一个子查询，测试行是否存在。

Transact-SQL 语法约定

语法

EXISTS subquery

参数

subquery

受限制的 SELECT 语句。不允许使用 COMPUTE 子句和 INTO 关键字。有关详细信息，请参阅 SELECT (Transact-SQL) 中有关子查询的信息。

结果类型

Boolean

结果值

如果子查询包含任何行，则返回 TRUE。

示例

A. 在子查询中使用 NULL 仍然返回结果集

以下示例返回在子查询中指定了 NULL 的结果集，并且通过使用 EXISTS 仍求值为 TRUE。

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USE AdventureWorks ; GO SELECT DepartmentID, Name FROM HumanResources.Department WHERE EXISTS (SELECT NULL) ORDER BY Name ASC ;

B. 比较使用 EXISTS 和 IN 的查询

以下示例比较了两个语义等同的查询。第一个查询使用 EXISTS，第二个查询使用 IN。

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USE AdventureWorks ; GO SELECT DISTINCT c.FirstName, c.LastName, e.DepartmentID FROM Person.Contact c JOIN HumanResources.Employee e ON e.ContactID = c.ContactID WHERE EXISTS (SELECT * FROM HumanResources.Department d WHERE e.DepartmentID = d.DepartmentID AND d.Name = 'Purchasing') ; GO

下面的查询使用 IN。

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USE AdventureWorks ; GO SELECT DISTINCT c.FirstName, c.LastName, e.DepartmentID FROM Person.Contact c JOIN HumanResources.Employee e ON e.ContactID = c.ContactID WHERE DepartmentID IN (SELECT DepartmentID FROM HumanResources.Department d WHERE d.Name = 'Purchasing') ; GO

以下是其中任一查询的结果集。

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FirstName LastName DepartmentID ------------------------- ------------------------- ------------ Annette Hill 5 Arvind Rao 5 Ben Miller 5 Eric Kurjan 5 Erin Hagins 5 Frank Pellow 5 Fukiko Ogisu 5 Gordon Hee 5 Linda Meisner 5 Mikael Sandberg 5 Reinout Hillmann 5 Sheela Word 5 (12 row(s) affected)

C. 比较使用 EXISTS 和 = ANY 的查询

以下示例显示两个查找其名称与供应商名称相同的商店的查询。第一个查询使用 EXISTS，第二个查询使用 = ANY。

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USE AdventureWorks ; GO SELECT DISTINCT s.Name FROM Sales.Store s WHERE EXISTS (SELECT * FROM Purchasing.Vendor v WHERE s.Name = v.Name) ; GO

下面的查询使用 = ANY。

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USE AdventureWorks ; GO SELECT DISTINCT s.Name FROM Sales.Store s WHERE s.Name = ANY (SELECT v.Name FROM Purchasing.Vendor v ) ; GO

D. 比较使用 EXISTS 和 IN 的查询

以下示例显示查找以 P 开头的部门员工的查询。

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USE AdventureWorks; GO SELECT c.FirstName, c.LastName, e.Title FROM Person.Contact c JOIN HumanResources.Employee e ON e.ContactID = c.ContactID WHERE EXISTS (SELECT * FROM HumanResources.Department d WHERE e.DepartmentID = d.DepartmentID AND d.Name LIKE 'P%'); GO

下面的查询使用 IN。

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USE AdventureWorks; GO SELECT c.FirstName, c.LastName, e.Title FROM Person.Contact c JOIN HumanResources.Employee e ON e.ContactID = c.ContactID WHERE DepartmentID IN (SELECT DepartmentID FROM HumanResources.Department WHERE Name LIKE 'P%'); GO

E. 使用 NOT EXISTS

NOT EXISTS 的作用与 EXISTS 正相反。如果子查询没有返回行，则满足 NOT EXISTS 中的 WHERE 子句。以下示例查找不在部门中且姓名以 P 开头的员工。

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USE AdventureWorks; GO SELECT c.FirstName, c.LastName, e.Title FROM Person.Contact c JOIN HumanResources.Employee e ON e.ContactID = c.ContactID WHERE NOT EXISTS (SELECT * FROM HumanResources.Department d WHERE e.DepartmentID = d.DepartmentID AND d.Name LIKE 'P%') ORDER BY LastName, FirstName GO

下面是结果集： 

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FirstName LastName Title ------------------------------ ------------------------------ ------------ Syed Abbas Pacific Sales Manager Hazem Abolrous Quality Assurance Manager Humberto Acevedo Application Specialist Pilar Ackerman Shipping & Receiving Superviso François Ajenstat Database Administrator Amy Alberts European Sales Manager Sean Alexander Quality Assurance Technician Pamela Ansman-Wolfe Sales Representative Zainal Arifin Document Control Manager David Barber Assistant to CFO Paula Barreto de Mattos Human Resources Manager Shai Bassli Facilities Manager Wanida Benshoof Marketing Assistant Karen Berg Application Specialist Karen Berge Document Control Assistant Andreas Berglund Quality Assurance Technician Matthias Berndt Shipping & Receiving Clerk Jo Berry Janitor Jimmy Bischoff Stocker Michael Blythe Sales Representative David Bradley Marketing Manager Kevin Brown Marketing Assistant David Campbell Sales Representative Jason Carlson Information Services Manager Fernando Caro Sales Representative Sean Chai Document Control Assistant Sootha Charncherngkha Quality Assurance Technician Hao Chen HR Administrative Assistant Kevin Chrisulis Network Administrator Pat Coleman Janitor Stephanie Conroy Network Manager Debra Core Application Specialist Ovidiu Crãcium Sr. Tool Designer Grant Culbertson HR Administrative Assistant Mary Dempsey Marketing Assistant Thierry D'Hers Tool Designer Terri Duffy VP Engineering Susan Eaton Stocker Terry Eminhizer Marketing Specialist Gail Erickson Design Engineer Janice Galvin Tool Designer Mary Gibson Marketing Specialist Jossef Goldberg Design Engineer Sariya Harnpadoungsataya Marketing Specialist Mark Harrington Quality Assurance Technician Magnus Hedlund Facilities Assistant Shu Ito Sales Representative Stephen Jiang North American Sales Manager Willis Johnson Recruiter Brannon Jones Finance Manager Tengiz Kharatishvili Control Specialist Christian Kleinerman Maintenance Supervisor Vamsi Kuppa Shipping & Receiving Clerk David Liu Accounts Manager Vidur Luthra Recruiter Stuart Macrae Janitor Diane Margheim Research & Development Enginee Mindy Martin Benefits Specialist Gigi Matthew Research & Development Enginee Tete Mensa-Annan Sales Representative Ramesh Meyyappan Application Specialist Dylan Miller Research & Development Manager Linda Mitchell Sales Representative Barbara Moreland Accountant Laura Norman Chief Financial Officer Chris Norred Control Specialist Jae Pak Sales Representative Wanda Parks Janitor Deborah Poe Accounts Receivable Specialist Kim Ralls Stocker Tsvi Reiter Sales Representative Sharon Salavaria Design Engineer Ken Sanchez Chief Executive Officer Jos? Saraiva Sales Representative Mike Seamans Accountant Ashvini Sharma Network Administrator Janet Sheperdigian Accounts Payable Specialist Candy Spoon Accounts Receivable Specialist Michael Sullivan Sr. Design Engineer Dragan Tomic Accounts Payable Specialist Lynn Tsoflias Sales Representative Rachel Valdez Sales Representative Garrett Vargar Sales Representative Ranjit Varkey Chudukatil Sales Representative Bryan Walton Accounts Receivable Specialist Jian Shuo Wang Engineering Manager Brian Welcker VP Sales Jill Williams Marketing Specialist Dan Wilson Database Administrator John Wood Marketing Specialist Peng Wu Quality Assurance Supervisor (91 row(s) affected)