两个sql表的join

Question

I have two tables and I want to join them to get the desired output. Say the 1st table (seat1) is

and the 2nd table (collegestudents) is

The desired output is

I have tried the below code. But it fails to give the desired result.

    $rde2=mysqli_query($con, "select * from seat1 s
                              left JOIN collegestudents c ON c.Roll = s.Roll
                              ");            




     Any help please.

Answer 1

You want a left join . Your query looks fine, but you would need not to use select * , and instead explictly list the columns that you want to select, using table prefixes. Otherwise, since you have a Roll column in both tables, a name clashes will happen, that your application apparently does not handle well.

select 
    s.Roll,
    c.Name,
    s.Subject
from seat1 s
left join collegestudents c on c.Roll = s.Roll