Question

I do file parsing in Perl and insert into a table in a MySQL database. For example, I have the following fields:

S.No ,PCID,USERNAME, TIME   INFORMATION.
1     203  JANE      22:08  updation
2     203  JANE      22:09  deletion
3     203  JANE      22:10  insertion

In this table I wanted to have the PCID to be unique, USERNAME to be unique. S.No is unique, since I have set it to autonumbering and it’s the primary key. Now my question is:

If I add PCID and USERNAME as composite primary key, I still find duplicates in the table. There is no change. The same o/p. What should be done to remove the duplicate? Should I code in Perl to check for duplicates before insertion?

Please guide and provide assistance. Thanks in advance.

Answer 1

You want the S.No to remain the primary key and PCID + USERNAME to be unique, so close to what Hammerite said:

ALTER TABLE MyTable
    ADD PRIMARY KEY (`S.No`),
    ADD UNIQUE KEY `PCID_USER_uk` (`PCID`, `USERNAME`);