Problem with the primary key

Question

Hi All,
I have a table with the same data repeating 2 times. I mean the rows are depating twice. so now I am creating primary key to the table. It is throwing me an error saying primary key voilation. I will provide the clear scenario.
create table Employee(
ID VARCHAR2(4 BYTE) NOT NULL,
First_Name VARCHAR2(10 BYTE),
Last_Name VARCHAR2(10 BYTE),
Start_Date DATE,
End_Date DATE,
Salary Number(8,2),
City VARCHAR2(10 BYTE),
Description VARCHAR2(15 BYTE)
insert into employee values ('01','Jason', 'Martin', to_date('19960725','YYYYMMDD'), to_date('20060725','YYYYMMDD'), 1234.56, 'Toronto', 'Programmer');
insert into employee values ('02','Alison', 'Mathews', to_date('19760321','YYYYMMDD'), to_date('19860221','YYYYMMDD'), 6661.78, 'Vancouver','Tester');
insert into employee values ('03','James', 'Smith', to_date('19781212','YYYYMMDD'), to_date('19900315','YYYYMMDD'), 6544.78, 'Vancouver','Tester');
insert into employee values ('04','Celia', 'Rice', to_date('19821024','YYYYMMDD'), to_date('19990421','YYYYMMDD'), 2344.78, 'Vancouver','Manager');
insert into employee values ('05','Robert', 'Black', to_date('19840115','YYYYMMDD'), to_date('19980808','YYYYMMDD'), 2334.78, 'Vancouver','Tester');
insert into employee values ('07','David', 'Larry', to_date('19901231','YYYYMMDD'), to_date('19980212','YYYYMMDD'), 7897.78,'New York', 'Manager');
insert into employee values ('06','Linda', 'Green', to_date('19870730','YYYYMMDD'), to_date('19960104','YYYYMMDD'), 4322.78,'New York', 'Tester');
insert into employee values ('08','James', 'Cat', to_date('19960917','YYYYMMDD'), to_date('20020415','YYYYMMDD'), 1232.78,'Vancouver', 'Tester')
insert into employee values ('07','David', 'Larry', to_date('19901231','YYYYMMDD'), to_date('19980212','YYYYMMDD'), 7897.78,'New York', 'Manager');
insert into employee values ('06','Linda', 'Green', to_date('19870730','YYYYMMDD'), to_date('19960104','YYYYMMDD'), 4322.78,'New York', 'Tester');
Now the table is with 10 columns
ID FIRST_NAME LAST_NAME START_DAT END_DATE SALARY CITY DESCRIPTION
01 Jason Martin 25-JUL-96 25-JUL-06 1234.56 Toronto Programmer
02 Alison Mathews 21-MAR-76 21-FEB-86 6661.78 Vancouver Tester
03 James Smith 12-DEC-78 15-MAR-90 6544.78 Vancouver Tester
04 Celia Rice 24-OCT-82 21-APR-99 2344.78 Vancouver Manager
05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver Tester
06 Linda Green 30-JUL-87 04-JAN-96 4322.78 New York Tester
07 David Larry 31-DEC-90 12-FEB-98 7897.78 New York Manager
08 James Cat 17-SEP-96 15-APR-02 1232.78 Vancouver ester
Creating Primary key to the table
"ALTER TABLE employee PRIMARY KEY ( ID, First_Name, Last_Name, Start_Date, End_Date,
Salary, City, Description );"
I am getting primary key voilation error
IS THERE ANY WAY TO CREATE PRIMARY KEY ON THE TABLE WITH OUT DELETING THE DATA?
iS IT POSSIBLE CREATING PRIMARY KEY BY USING 'GROUP BY' FUNCTION OR ANY OTHER FUNCTIONS?
Edited by: user11872870 on Sep 23, 2010 5:41 PM

Answer 1

user11872870 wrote:
Actually there is a small mistake in the question. The table is having the data as
ID FIRST_NAME LAST_NAME START_DAT END_DATE SALARY CITY DESCRIPTION
01 Jason Martin 25-JUL-96 25-JUL-06 1234.56 Toronto Programmer
02 Alison Mathews 21-MAR-76 21-FEB-86 6661.78 Vancouver Tester
03 James Smith 12-DEC-78 15-MAR-90 6544.78 Vancouver Tester
04 Celia Rice 24-OCT-82 21-APR-99 2344.78 Vancouver Manager
05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver Tester
06 Linda Green 30-JUL-87 04-JAN-96 4322.78 New York Tester
07 David Larry 31-DEC-90 12-FEB-98 7897.78 New York Manager
08 James Cat 17-SEP-96 15-APR-02 1232.78 Vancouver ester
05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver "NULL"
06 Linda Green 30-JUL-87 04-JAN-96 4322.78 New York "NULL"
There is a null in the duplicate data.....
As there is NULL in the data It is not allowing me to add the primary key to the table.....
I am just looking if there is any other way to create primary key with the same data....the reason for the null not allowing you to have unique records is because null means "unknown". I could go into this in more depth but....
...again - we need to ask, why do you have linda green and robert black in there twice.
if you really do need those two extra rows, then create another column with a unique ID using a sequence and make that the primary key. a primary key uniquely identifies a row. for this data I don't see any reason whatsoever to create a composite key like you are attempting.
by trying to make the entire row a primary key it is clear your understanding is severely lacking.