add data into primary key : <p>this is my table.In this table i want to add a primary key column name "emp_id" as the first column .I don't know how to do it .So,can you please help me! </p>

<pre><code>EMP_NAME             EMP_POS            SALARY           GENDER 
----------------- ----------------- --------------      ------ 
anand              worker             10000                 M      
balu               manager            50000                 M      
carl               manager            50000                 M      
riya               md                 60000                 F      
prabhu             owner              99999999              M      
</code></pre>
