Answer / upendra

Primary key creates Clustered Indexes. Clustered indexes physically sort the data.
Unique can have only Non-clustered indexes, where data are not physically sorted.

Answer / shahid

the above answer is wrong ...we can use foreign key for
unique key also...

Answer / aritra biswas

With the creation of primary key the oracle server
automatically creates and maintains a index on the primary
key column(s). Because of that index, the searching
processes on that table will be very fast where as
declaring a column as a (unique+not null) will not create
any index on that colum(s).It has to be created manually by
the DBA/users if we wish to enhance the searching process.

Answer / prativa mishra

We can create more unique key in a table but we can not create more then one primary key in a table.At the time of primary key creation thr is a clusterd index created automatically and it sorts data physically. It helps in searching process which not possible in unique+notnull column

Answer / joshy joy

1. Primary key creates Clustered Indexes and they are physically sort the data.
2. Oracle server automatically creates and maintains an index on the primary key and because of that searching will be very fast on that table.
3. Primary can be used for referential integrity when dealing with foreign key in child table

1. Unique can have only Non-clustered indexes, where data are not physically sorted.
2. unique key + not null will not create any index on that column(s)
3. Key column should be Primary key column in parent table when when dealing with foreign key

Answer / john

primary key will not allow null values.but in case of
unique,more than one null value s accepted.

Answer / banti

Both r same :)
Primary Key= (Unique + Not Null)

Answer / gazulas

if it is Primary key then we can make use foreign key in other table and can use the referential integrity concept

for unique keys we dont have that.

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Hi, I am new in oracle(SQL), could anyone help me in writing a correct SQL. Below is the table structure. Table: Subsc Fields: 1. Sub_no (this field will hold values of subscriber nos, for e.g. S111111, S222222, S333333, S444444, etc.) 2. s_status (this field will hold values for different status of subscriber, for e.g. 'A', 'S', 'C', etc.) 3. cus_id (this field will hold values of bill nos for e.g. 11111111, 22222222, 33333333, 44444444, etc.) Table: Bill Fields: 1. Bill_no this field will hold values of bill nos for e.g. 11111111, 22222222, 33333333, 44444444, etc.) 2. b_status = (this field will hold values for different status of bill for e.g. 'O', 'C', 'S', etc.) Note: 1. The Sub_no is a Primary key of Subsc table. 2. The cus_id is a foreign in Subsc table (referred from Bill_no field of Bill table) 3. The Bill_no field is the Primary key of Bill table. Query A --> I wrote a query to select cus_id/Bill_no which is in status open (b_status = 'O') and having more than two active subscriber (i.e. S_status = 'A') in it ( i.e. more the two subscribers in same bill). select s.cus_id from subsc s where exists (select 1 from bill where bill_no = s.cus_id and b_status = 'O') and s_status = 'A' group by s.cus_id having count(sub_no) = 2 Problem : The above query will give the cus_id (or rather bill_no) which are in open status (b_status ='O) and which are having TWO ACTIVE Subscribers (s_status ='A') in it. However, this query will also lists the cus_id/bill_no which are having more than TWO subscribers in it (but only two subscriber will be in Active status (s_status = 'A') and the others will be in s_status = 'C' or s_status = 'S'. Help needed: I want to write a query which will fetch ONLY the cus_id/bill_no which are in open status (b_status ='O') and which are having ONLY TWO ACTIVE subscribers (s_status ='A') in it. B--> If I include the sub_no in the above query then NO row are returned. select s.cus_id, s.sub_no from subsc s where exists (select 1 from bill where bill_no = s.cus_id and b_status = 'O') and s_status = 'A' group by s.cus_id, s.sub_no having count(sub_no) = 2 Help needed: I want to modify the above query which will fetch ONLY the cus_id/bill_no which are in open status (b_status ='O') and which are having ONLY TWO ACTIVE subscribers (s_status ='A') in it ALONG with the sub_no. Thanks a lot in advance. Regards, Nitin

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