Joining two tables - php

Question

I am trying to join a dataofbirth column which is in studentdetails table with another table called college table, I need the dataofbirth of the student in the second table.Here is my query.
$result = mysqli_query($con,"SELECT `DateofBirth` FROM `studentdetails` INNER JOIN `college`
ON `studentdetails`.StudentID = college.StudentID")or die ("Error: ".mysqli_error($con)");
So when I fetch my array for the second table I would be able to get their dataofBirth of student without joining them physically.
Can anyone spot what's wrong with my syntax ?
Thank you

Answer 1

If you want to join two tables you have to provide the list of columns from both tables that you want to be included in joined/combined table. So:
Try this (substituting [add other columns..] bit with the other columns you might want to include. And take note of the table aliases how they are being used:
$result = mysqli_query($con,"SELECT s.DateofBirth, c.StudentID, [add other columns from college table here...] FROM studentdetails sd INNER JOIN college c
ON sd.StudentID = c.StudentID")or die ("Error: ".mysqli_error($con)");
oh and you might want to use mysqli instead of old, deprecated, ugly, slow, insecure, suicidal thoughts inducing mysql_ extension ;)

Answer 2

It should be (from the comment : dateofbirth only exists in the studentdetails )
$result = mysqli_query($con,"SELECT sd.DateofBirth FROM studentdetails as sd INNER JOIN college as c
ON sd.StudentID = c.StudentID")or die ("Error: ".mysqli_error($con)");

Answer 3

Considering that we born only once (except for phoenixes) the relationship between students and their date of birth is supposed to be 1:1 relationship. In other words, column DateOfBirth could be declared in college table. Then to select their date of birth you simple could do:
select DateOfBirth
from college
where StudentID = :id
But I see you already have another table to store their date of birth so you could do a join to select their date of birth:
select d.DateOfBirth
from college c,
studentdetails d
where c.StudentID = d.StudentID;
Or:
select d.DateofBirth
from studentdetails d
inner join college as c
on d.StudentID = c.StudentID;
But this queries above would exclude the students without records in studentdetails from your result. To select all students with their respective date of birth you could do:
select c.StudentID,
s.DateOfBirth
from studentdetails d
right join college c
on d.StudentID = c.StudentID;
This right join query gets all the students even if they don't have a date of birth in studentdetails table (right join cmd on table college).
You're free to figure out what's the best alternative to you, but I recommend you to normalize this data model putting column DateOfBirth inside college table.