How to create composit key ??

Question

Hello Friends!
i need your help. I have to create composit key.
I have 2 tables. Table 1 contains 9 colums and table 2 contains 3 colums. I am writing down just related colums of table1
Table1: SID (pk) , Bytes_convert_test , Operator , Value , offset_test , Bytes_convert_jump , offset_jump
Table2: SID (fk) , value , type , ID (pk)
in table2 type represents the 2 colums in table 1 (Bytes_convert_test and Bytes_convert_jump). Type colum could be anyone of them may be for one record it is Bytes_convert_test or for another record bytes_convert_jump. values
Value colum in table2 having different values or may be same values for both records. but my task is that i have to store record like if the type in table2 is bytes_to_convert then the values colum stores values for bytes to convert record. In short i have to separate values according to type. I am not sure that i need SID as fk in table2.
Remember value colum in table1 containing different entries.
Waiting for quick reply.
BR,
Zeeshan
Edited by: user10899712 on 2009-apr-20 03:42

Answer 1

Hello Zeeshan,
You are saying you want to use Type and Value fields in Table2 as foreign keys to Table1 and based on logical operations,Type maps to Bytes_convert_test and/or Bytes_convert_jump in Table1. This means that there is no way to do a straight join between Table1 and Table2 that I can see. Unless you have some simple logic you can add to a query to get the joins to work consistently, I would strongly recommend you use a simple foreign key in Table2.
Using a simple foreign key that goes to Table1's primary key not only makes the table joins easier, it also will reduce database hits - since now the primary key can be used when traversing relationships to search the cache instead of having to always go to the database.
Best Regards,
Chris