I am a novice at SQL and Php. I am making weekly rota.

I have managed to duplicate a SQL database row in a table using this code below.

INSERT 
    
SELECT 
   
FROM 

WHERE

I have modified the above code to include SQL CASE as you can see below, so I can apply a condition to the "weekstart" column. I want to be able to set a condition of, if weekstart date in sql database = $dateone variable then apply $datethree variable or if weekstart date in sql database = $datetwo variable then apply $datefour variable. The modification will be applied to the duplicated row. many thanks.

$dateone = "2026-03-02";
$datetwo = "2026-03-09";

$datethree ="2026-03-16";
$datefour = "2026-03-23";


$sql = "INSERT INTO myrota (weekstart)
SELECT weekstart,

CASE
                WHEN weekstart= '$dateone' THEN '$datethree'
                WHEN weekstart= '$datetwo' THEN  '$datethree'
                
                ELSE 'empty'
             
            END AS weekstart
          
            
FROM myrota ";