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concatenated keys in Sybase SQLANYwhere

Posted on 1998-03-17
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Last Modified: 2008-03-10
CREATE TABLE emp_skill(
emp_id INTEGER NOT NULL,
skill_id INTEGER NOT NULL,
"skill level" INTEGER NOT NULL,
PRIMARY KEY( emp_id, skill_id ),
FOREIGN KEY REFERENCES employee,
FOREIGN KEY REFERENCES skill
)
----------------------------------
how does a "concatenated" key work in the above example? if you want to link to it from another table -- u have gotta have a 'concatenated' key there too? u obviously can't join to the above table if u got only emp-id..

if i use SQLCentral i can't get to see/define if the combination of both is unique or not.

if this concatenated key is a foreign key somewhere else - how is it implemented?
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Question by:hunchback
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jbiswas earned 200 total points
ID: 1098366
The proper term for a primary key consisting of two or more fields is a composite key. I assume we are talking about the same thing. When you set something as a primary key it has to be unique. So by default it will not allow any duplicate values. In isql you can do a duplicate check(which you will not find in case of a primary key) with a queruy of the following format:
select count(*), field_name1, field_name2 from table_name group by field_name1, field_name2 having count(*)>1
To make this a foreign key for some table, that table should have these two fields and under that table , go to foreign key, add foreign key and when it asks for the talename and column_names, give the appropriate table name and the name of the two columns. That should make this composite key a foreign key.
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by:hunchback
ID: 1098367
thanks very much ,Jbiswas, if u can made a comment:
when we have 2 fields like above example: is it normal/necessary in the sybaseDB realm or from your experience to create an additional/new  field call EmpSkillID (size=both fields added up)
and call a trigger to add both fields (empID, skillID) in order to define the value. Also making EmpSkillID the primary key.
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Expert Comment

by:jbiswas
ID: 1098368
Nope you do not have to do that. A composite key works just fine. The data is stored as per the composite key, so it doesn't make any sense to concatenate the two fields.
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