Uniqueness between 3 fields

Question

Hi all...

 

I need a logic in SQL Server database end -

I have 4 master tables -

1. EmployeeMaster

1 - Abhineet

2 - Neha

3 - Jaya

etc - 55 employees (1,2,3 - auto increment primary key)

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2. SubjectMaster 

1 - Java

2 - Project Management

3 - Time Management

4 - Oracle 

etc - 100 subjects(1,2,3,4 - auto increment primary key)

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3. OtherSubjectMasters

1- AJAX

2 -Query String

etc - 90 records (1,2,3... auto increment primary key)

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4. Ouarters -

Q1(April2016-June-2016)

Q2(July2016-September2016)

Q3(October2016-December2016)

Q4(January2017-March2017)

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Now, from front - end, the dropdownlist is binded with SubjectMaster.

Incase, the user wants to insert other subject (not present in SubjectMaster table, then he/she inserts othersubject in OtherSubjectMaster table)

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Transaction table -

ID	EmpID	SubjectID	OtherSubjectID	Quarter
1	1 (Abhineet)	1	0	Q3(October2016-December2016)
2	1 (Abhineet)	0	2	Q4(January2017-March2017)

 

Here, if user enters subject from dropdownlist(subjectmaster table), then "SubjectID" field will have the ID of Subject and OtherSubjectID will have 0.

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Logic that I need -

I want to check that one employee - is allowed to attend one training in one quarter.

Eg - here now, Abhineet will not be able to attend the training of subject id - 1 in Quarter-3 (Q3).

He may attend training of other subjects in this same quarter - Q3.

How do we get uniqueness between - Employee , Subject and Quarter ??

 

Please guide....