Application domain. Consider a simple banking application in which customers per

Question

Application domain. Consider a simple banking application in which customers perform transactions on some of their accounts. For this purpose we have the database schema that consists of the following three relation schemata: CUSTOMER Cid, name, phone ACCOUNT num, type, desc TRANSACTION num, type, cid, time, amount Domains of attributes have been omitted. The following relations constitute a database, which we denote by db. ACCOUNT CUSTOMER phone num type desc cid name cl Jack 02102205945 01 cheque expenses c2 Jill 02102205945 02 cheque expenses c3 Jill 02259682104 02 online expenses TRANSACTION num type cid time amount 01 cheque cl 24-03-14 09:32 100 01 cheque cl 24-03-14- 22:11 100 02 cheque c2 24-03-14- 22:11 100 02 online c3 24-03-14- 22:11 +100

Explanation / Answer

Option 4 is true because if we join only Transaction and customer then some time possible that many num have type online so we first find type="online" from accountt and then match them with num and type of Transaction table and find the matched cid then we find record from customer table using cid.

name   (cid(CUSTOMER)num,type(ACCOUNT)num,type,cid(type="online"(TRANSACTION))).

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