EXISTS (Transact-SQL)
指定測試資料列是否存在的子查詢。
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語法
EXISTS subquery
引數
- subquery
這是受限制的 SELECT 陳述式。不允許使用 COMPUTE 子句和 INTO 關鍵字。如需詳細資訊，請參閱＜SELECT (Transact-SQL)＞中子查詢的相關資訊。
結果類型
Boolean
結果值
如果子查詢包含任何資料列，便傳回 TRUE。
範例
A. 在子查詢中使用 NULL，仍會傳回結果集
下列範例在子查詢中指定 NULL 來傳回結果集，使用 EXISTS 仍會評估為 TRUE。
USE AdventureWorks ;
GO
SELECT DepartmentID, Name
FROM HumanResources.Department
WHERE EXISTS (SELECT NULL)
ORDER BY Name ASC ;
B. 利用 EXISTS 和 IN 來比較查詢
下列範例比較語意相等的兩項查詢。第一項查詢使用 EXISTS，第二項查詢使用 IN。
USE AdventureWorks ;
GO
SELECT a.FirstName, a.LastName
FROM Person.Contact AS a
WHERE EXISTS
(SELECT *
FROM HumanResources.Employee AS b
WHERE a.ContactId = b.ContactID
AND a.LastName = 'Johnson');
GO
下列查詢使用 IN。
USE AdventureWorks ;
GO
SELECT a.FirstName, a.LastName
FROM Person.Contact AS a
WHERE a.LastName IN
(SELECT a.LastName
FROM HumanResources.Employee AS b
WHERE a.ContactId = b.ContactID
AND a.LastName = 'Johnson');
GO
以下是任何一項查詢的結果集。
FirstName LastName
-------------------------------------------------- ----------
Barry Johnson
David Johnson
Willis Johnson
(3 row(s) affected)
C. 利用 EXISTS 和 = ANY 來比較查詢
下列範例會顯示兩項查詢，它們用來尋找與供應商同名的商店。第一項查詢使用 EXISTS，第二項查詢使用 =ANY。
USE AdventureWorks ;
GO
SELECT DISTINCT s.Name
FROM Sales.Store AS s
WHERE EXISTS
(SELECT *
FROM Purchasing.Vendor AS v
WHERE s.Name = v.Name) ;
GO
下列查詢使用 = ANY。
USE AdventureWorks ;
GO
SELECT DISTINCT s.Name
FROM Sales.Store AS s
WHERE s.Name = ANY
(SELECT v.Name
FROM Purchasing.Vendor AS v ) ;
GO
D. 利用 EXISTS 和 IN 來比較查詢
下列範例會顯示尋找開頭是 P 之部門員工的查詢。
USE AdventureWorks;
GO
SELECT c.FirstName, c.LastName, e.Title
FROM Person.Contact AS c
JOIN HumanResources.Employee AS e
ON e.ContactID = c.ContactID
WHERE EXISTS
(SELECT *
FROM HumanResources.Department AS d
JOIN HumanResources.EmployeeDepartmentHistory AS edh
ON d.DepartmentID = edh.DepartmentID
WHERE e.EmployeeID = edh.EmployeeID
AND d.Name LIKE 'P%');
GO
下列查詢使用 IN。
USE AdventureWorks;
GO
SELECT c.FirstName, c.LastName, e.Title
FROM Person.Contact AS c JOIN HumanResources.Employee AS e
ON e.ContactID = c.ContactID
JOIN HumanResources.EmployeeDepartmentHistory AS edh
ON e.EmployeeID = edh.EmployeeID
WHERE edh.DepartmentID IN
(SELECT DepartmentID
FROM HumanResources.Department
WHERE Name LIKE 'P%');
GO
E. 使用 NOT EXISTS
NOT EXISTS 的作用與 EXISTS 相反。如果子查詢未傳回任何資料列，便滿足 NOT EXISTS 中的 WHERE 子句。下列範例會尋找不在部門中，且名稱開頭是 P 的員工。
SELECT c.FirstName, c.LastName, e.Title
FROM Person.Contact AS c
JOIN HumanResources.Employee AS e
ON e.ContactID = c.ContactID
WHERE NOT EXISTS
(SELECT *
FROM HumanResources.Department AS d
JOIN HumanResources.EmployeeDepartmentHistory AS edh
ON d.DepartmentID = edh.DepartmentID
WHERE e.EmployeeID = edh.EmployeeID
AND d.Name LIKE 'P%')
ORDER BY LastName, FirstName
GO
以下為結果集：
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
José 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)