Joined 3 tables, not outputting all results from third table? - mysql

Question

I have three tables:
Student - UPN, Name, Year, House
Seclusion_Status - ID, Arrived, FTE, Rebuild, DateTimeAdded, Staff, Student_UPN (fk), Comment
Period_Rating - ID, Slot_ID, Rating, Date, Seclusion_ID (fk)
Each student can have many entries in the Seclusion_Status table, and then there are also many entries in the Period_rating table, which is linked to the Seclusion_status table with the Seclusion_ID
I am running the following query to return a record from Seclusion_Status based on a date, and then all the records in the Period_rating table that relate to the Seclusion_status record.
$sql="SELECT * FROM Seclusion_Status
INNER JOIN Students ON Seclusion_Status.Student_UPN=Students.UPN
JOIN Period_Rating ON Seclusion_Status.ID=period_rating.Seclusion_ID
WHERE period_rating.Date = '$start'
GROUP BY period_rating.Seclusion_ID
ORDER BY Seclusion_Status.DateTimeAdded ASC";
$result=mysql_query($sql);
// Start looping rows in mysql database.
while($rows=mysql_fetch_array($result)){
The query is returning the Seclusion_Status record, and then the first record in Period_rating, but not the others.
Array
[0] => 348
[ID] => 157
[1] => Y
[Arrived] => Y
[2] => N
[FTE] => N
[3] =>
[Rebuild] =>
[4] =>
[Text] =>
[5] => 2016-03-04 09:30:50
[DateTimeAdded] => 2016-03-04 09:30:50
[6] => Mr S Holland
[Staff] => Mr S Holland
[7] => K80222800
[Student_UPN] => K8022280
[8] => Refusing instructions
[Incident] => Refusing instructions
[9] =>
[Period] =>
[10] =>
[Period_In_ID] =>
[11] => Not sitting properly in class despite being asked
[Comment] => Not sitting properly in class despite being asked
[12] => K80222800
[UPN] => K80222800
[13] => Student Name
[Name] => Student Name
[14] => Year 9
[Year] => Year 9
[15] => Acer
[House] => Acer
[16] => 157
[17] => P2
[Slot_ID] => P2
[18] =>
[Rating] =>
[19] => 2016-03-04
[Date] => 2016-03-04
[20] => 348
[Seclusion_ID] => 348
[21] => 1
[Status] => 1

Answer 1

The query is returning the Seclusion_Status record, and then the first record in Period_rating, but not the others.
You have a GROUP BY period_rating.Seclusion_ID that instructs mysql to return one record per Seclusion_ID. Take the group by clause out, and the query will return multiple records, that match.

Answer 2

The thing is if you use join, if data is there in all the three tables then only it will fetch.
If you want to fetch all the entries in the table you need to use outer join, unfortunately u cant use outer join in mysql.
but you can fetch results by unioning leftjoin results and right join results