creating a unique column in Linux (more like an sql primary key?)

Question

so i am new to Linux and our instructor gave us this assignment, its fairly simple but I haven't been able to create a unique column for my 'employee code' (we need this in order to avoid duplicating codes) I tried two methods below

Method 1

    echo "Enter an Employee Code:
 read code
    if [$code uniq -u]
 then
    echo "Enter surname"
 read surname
    echo "Enter Other names"
 read other_names
    echo "Choose Gender"
    echo "f Female  m male"
 read gender
    case $gender in

         f) Female;;
         m) Male;;
         *) echo" that was not one of the choices"
           esac
    echo " Enter DOB"
 read dob
    echo "Enter Phone Number"
 read phone_num
    echo "$code   $surname   $other_names   $gender   $dob" >> details

else echo "Duplicate employee code" fi

METHOD 2

     echo "Enter an Employee Code:
 read code
     while [ $code -ne $code ]
 do
     echo "Enter surname"
 read surname
     echo "Enter Other names"
 read other_names
     echo "Choose Gender"
     echo "f Female  m male"
 read gender
    case $gender in
          f) Female;;
          m) Male;;
          *) echo" that was not one of the choices"
            esac
   echo " Enter DOB"
 read dob
   echo "Enter Phone Number"
 read phone_num
   echo "$code   $surname   $other_names   $gender   $dob" >> details

else echo "Duplicate employee code"

done

can someone please help? method 1 doesn't recognize the "uniq" constraint while method 2 keeps increments non-stop. thanks a lot in advance :)