The problem about Relational Database

[tzungshianlin]

There are two tables:
Investigator (INO, Name, Salary, DNO)
Department (Dnumber, Dname)

They represent for:
Investigator (The identification number for investigator, The name for investigator, Salary, The number for department)
Department (The number for department, The name for department)

The question:
Please write down the SQL:
Focusing on "special" department employee whose salary is less than 30000, and adding additional 5% salary.

The answer is:
UPDATE Investigator
SET Salary= Salary*1.05
WHERE EXISTS(
SELECT*
FROM DEPARTMENT
WHERE Department.Dnumber= Investigator.DNO
AND Dname='special' AND Salary<30000

I can't understand this sentence:
WHERE Department.Dnumber= Investigator.DNO
Can anyone please tell me?
Thanks

 

[mmerlinn]

This appears to be a school assignment.

Read the RED sentence at the bottom of this page and read the posting guidelines.

Schoolwork is NOT ALLOWED on these forums.

mmerlinn

http://mmerlinn.com

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[johnherman]

the clause: WHERE Department.Dnumber= Investigator.DNO
is one of the constraints on the query that begins with the word SELECT

The three constraints following the WHERE clause are used to define the subset of records that will be affected by the UPDATE statement.

The query can be rewritten with an inner join instead of the "WHERE Department.Dnumber= Investigator.DNO" part of the WHERE clause:

UPDATE Investigator
SET Salary= Salary*1.05
WHERE Dname='special' AND Salary<30000
INNER JOIN Department ON
Department.Dnumber= Investigator.DNO


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[tzungshianlin]

Sorry, this is the question in uni but I will not post next time.