How to Create Unique Index for Existing table in MySQL which contains Records

Question

Here i like to explain my problem,

I Need to Create Unique Index in my Existing table, and the table contains many records.

I tried to execute this code

CREATE UNIQUE INDEX empid_name ON employee (importcompany_id, employee_id, name, relationship);

but am getting error as

#1062 - Duplicata du champ '0-Emp ID-Member Name-Relationship' pour la clef 'empid_name' 

Help me to sort out this problem, i need to make fields unique

Updated :

The reason for setting these fields unique is

Actually i have a table like this

id  company_ID  Employee_ID Name        Relationship    Dob     Age Gender       
1   EMPL        00001       Choodamani  Spouse      11-Aug-66   49  Female            
2   EMPL        00001       Komala      Mother      30-Oct-39   76  Female            
3   EMPL        00001       Varshini    Daughter    29-Apr-04   11  Female            
4   EMPL        00001       Vasudevan   Employee    15-Jul-62   53  Male    
5   EMPL        00002       Siddharth   Son         1-Jun-00    15  Male              
6   EMPL        00002       Poongavanam Mother      21-Oct-39   76  Female            
7   EMPL        00002       Aruna       Spouse      16-Sep-68   47  Female            
8   EMPL        00002       Abirami     Daughter    7-May-97    18  Female            
9   EMPL        00002       Murali      Employee    7-Oct-67    48  Male

if have insert a data like this,

    id  company_ID  Employee_ID Name        Relationship    Dob     Age Gender       
    1   EMPL        00001       Choodamani  Spouse      11-Aug-70   45  Female            
    2   EMPL        00001       Nirmal      Son      30-Oct-39   76  Female

this insert or update is done through import using excel sheet

Answer 1

1. If you want to have unique index empid_name ON employee table with columns (importcompany_id, employee_id, name, relationship). Then you must delete existing duplicate data.

Easy way to do this is to add a UNIQUE index on the 4 columns. When you write the ALTER statement, include the IGNORE keyword. Like so:

ALTER IGNORE TABLE `employee` ADD UNIQUE INDEX(importcompany_id, employee_id, name, relationship);

This will drop all the duplicate rows. As an added benefit, future INSERTs that are duplicates will error out. As always, you may want to take a backup before running something like this.

2. Or Add primary key in your table then you can easily remove duplicates from your table. And then add unique index.