Q:

How to insert into a database some information that can be the same that another row? 

Like, I have a row contain this information.  The hidden column determine if it’s visible in research (0) or not (1). 
I want to insert a new row with similar info (especially same name) of the row with hidden number =1.  But right now, if I insert same info of a computer that have an hidden number = 1 (like IT-Melanie), it will only ‘refresh’ the row already there, not created a new one!  It’s there a possibility to create a new row with the same name (like IT-Melanie), but with maybe some differents other infos to insert without this update the already existing row?  It’s like if we duplicate a row in the database, but with all the same information. 
The only think I found here it's duplicate a row in javascript and it's not I want.  I try to insert more than a time information to have two rows similar without success, only an update of the row already present in database! 
Recap : I want insert a new computer with same name of one already existing in the database, but the old one will have an hidden number = 1 and the new one = 0. 
Question : Can we put two row with the same computer_name without editing the old row? 
Example :
Old row : Computer_name = It_melanie
product_number= xxxxx-xxxxxx-xxxxx-xxxxxx-xxxxx
           [...]
           hidden=1
New row : Computer_name = It_melanie
product_number= xxxxx-xxxxxx-xxxxx-xxxxxx-xxxxx
           [...]
           hidden=0
Unique Key
My code 
    //Get informations in the form and insert it into db
    $location=$_GET['location'];
    $dept=$_GET['dept'];
    $jack=$_GET['jack'];
    $computername=$_GET['computername'];
    $productkey=$_GET['productkey'];
    $model=$_GET['model'];
    $vendor=$_GET['vendor'];
    $serialnumber=$_GET['serialnumber'];
    $macaddress=$_GET['macaddress'];
    $status=$_GET['status'];
    $starphone=$_GET['starphone'];
    $intid=$_GET['intid'];
    $did=$_GET['did'];
    $software=$_GET['software'];
    $query='insert into department(
    department,
    location_id)values(
    "'.$dept.'", 
    "'.$location.'")'; 
    if(valid_query($query)){
    $message .= "Enregistrement a ete mis a jour<br>";
    }else{
            $message .= "Enregistrement n a pas ete mis a jour!  S'il vous plait contacter le Departement TI IOS<br>";
    }
    $query='insert into computer(
    computer_name,
    product_key,
    model,
    serial_number,
    status_id,
    starphone,
    inst_id,
    did,
    macaddress,
    software_id,
    hidden
    )values(
    "'.$computername.'", 
    "'.$productkey.'", 
    "'.$model.'", 
    "'.$serialnumber.'", 
    "'.$status.'", 
    "'.$starphone.'", 
    "'.$intid.'", 
    "'.$did.'", 
    "'.$macaddress.'", 
    "'.$software.'", 
    0
    )';
    if(valid_query($query)){
    $message .= "Enregistrement a ete mis a jour<br>";
    }else{
            $message .= "Enregistrement n a pas ete mis a jour!  S'il vous plait contacter le Departement TI IOS<br>";
    }
    $query="select dept_id from department where department='$dept' and location_id='$location'";
    $deptid=select_query($query);
    $query="select computer_id from computer where computer_name ='$computername'";
    $computerid=select_query($query);
    $query='insert into jack(
    jack_number,
    dept_id,
    location_id,
    computer_id
    )values(
    "'.$jack.'", 
    "'.$deptid.'", 
    "'.$location.'", 
    "'.$computerid.'")'; 
    if(valid_query($query)){
    $message .= "Enregistrement a ete mis a jour<br>";
    }else{
            $message .= "Enregistrement n a pas ete mis a jour!  S'il vous plait contacter le Departement TI IOS<br>";
    }

    $query='insert into computer_vendor(
    computer_id,
    vendor_id
    )values(
    "'.$computerid.'", 
    "'.$vendor.'")'; 
    if(valid_query($query)){
    $message .= "Enregistrement a ete mis a jour<br>";
    }else{
            $message .= "Enregistrement n a pas ete mis a jour!  S'il vous plait contacter le Departement TI IOS<br>";
    }
    $location="";
    $dept="";
    $jack="";
    $computername="";
    $productkey="";
    $model="";
    $vendor="";
    $serialnumber="";
    $macaddress="";
    $status="";
    $starphone="";
    $intid="";
    $did="";

A:

First, make sure that the column computer_name is not marked as UNIQUE. 
-To do that connect to MySQL through Terminal or cmd or any shell, login in the database where the table is. ( run mysql -u <mysql_user> -p <db_name>) Then use DESCRIBE <table_name>; and in the column with value Key check is computer_name's value is UNI - this means that it is marked as UNIQUE.  Example result: img

Second, remove the UNIQUE constraint from the column. 

-To do that (while you are still connected to MySQL through shell and you are still in the same database) use ALTER TABLE <table_name> DROP INDEX computer_name;. 
Third, check did you succeed. 
-Again use DESCRIBE <table_name>; and if there is still a value UNI in the Key column do step 2 again. Good luck.