EXISTS (Transact-SQL)
Especifica una subconsulta para probar la existencia de filas.
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Sintaxis
EXISTS subquery
Argumentos
- subquery
Es una instrucción SELECT restringida. La cláusula COMPUTE y la palabra clave INTO no están permitidas. Para obtener más información, vea la información acerca de las subconsultas que aparece en SELECT (Transact-SQL).
Tipos de resultado
Boolean
Valores de resultado
Devuelve TRUE si una subconsulta contiene filas.
Ejemplos
A. Utilizar NULL en una subconsulta para seguir devolviendo un conjunto de resultados
En el ejemplo siguiente se devuelve un conjunto de resultados con NULL especificado en la subconsulta, que se sigue evaluando como TRUE al utilizar EXISTS.
USE AdventureWorks ;
GO
SELECT DepartmentID, Name
FROM HumanResources.Department
WHERE EXISTS (SELECT NULL)
ORDER BY Name ASC ;
B. Comparar consultas mediante EXISTS e IN
En el ejemplo siguiente se comparan dos consultas que son semánticamente equivalentes. En la primera consulta se utiliza EXISTS y en la segunda 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
En la siguiente consulta se utiliza 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
Éste es el conjunto de resultados de las consultas.
FirstName LastName
-------------------------------------------------- ----------
Barry Johnson
David Johnson
Willis Johnson
(3 row(s) affected)
C. Comparar consultas mediante EXISTS y = ANY
En el ejemplo siguiente se muestran dos consultas para buscar tiendas cuyo nombre sea el mismo que el de un proveedor. En la primera consulta se utiliza EXISTS y en la segunda =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
En la siguiente consulta se utiliza = 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. Comparar consultas mediante EXISTS e IN
En el siguiente ejemplo se muestran consultas para buscar empleados de departamentos que comiencen por P.
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
En la siguiente consulta se utiliza 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. Utilizar NOT EXISTS
NOT EXISTS funciona de forma contraria a EXISTS. La cláusula WHERE de NOT EXISTS se cumple si la subconsulta no devuelve ninguna fila. En el siguiente ejemplo se buscan empleados que no sean de departamentos cuyos nombres empiecen por P.
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
Éste es el conjunto de resultados.
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)