getting fieldname from multiple tables depending on condition - mysql

Question

I have the following mysql query:
SELECT
u.ID,
u.StudentCode,
c.classname,
s.STUDENTNAME,
u.UserCode,
g.ForeName AS MessageSentBy,
u.Message,
u.ForTchrSname AS MessageSentTo,
DATE_FORMAT(u.datetime, '%d-%m-%y') AS datesent,
u.RecordStatus
FROM
tblupdates u,
tblguardian g,
tblstudent s,
tblclass c
WHERE u.UserCode = g.GuardianCode
AND u.StudentCode = s.STUDENTCODE
AND (
YEAR(u.DateTime) = '2013'
AND MONTH(u.DateTime) = '09'
)
AND u.RecordStatus = 'N'
AND c.classcode = s.classcode
ORDER BY u.datetime DESC
Result of this query is shown below:
Now in my tblupdates for year-2013 and month-09 i have the following rows:
Now in my above result i am getting data for id=138 but i want to display all.The reason for not displaying other rows is that (usercode-30000,admin) these occur in tblteacher rather than tblguardian.So now i want that if the usercode is from tblguardian it shows guardian name but if it is from tblteacher it shows teachername but shows all the rows.Tblteacher and tblupdates can be joined by teachercode and usercode respectively.
I tried the following query but it doesnot return any row:
SELECT
u.ID,
u.StudentCode,
c.classname,
s.STUDENTNAME,
u.UserCode,
IF(
u.usercode NOT IN (g.guardiancode),
t.teachername,
g.ForeName
) AS MessageSentBy,
u.Message,
u.ForTchrSname AS MessageSentTo,
DATE_FORMAT(u.datetime, '%d-%m-%y') AS datesent,
u.RecordStatus
FROM
tblupdates u,
tblguardian g,
tblstudent s,
tblclass c,
tblteacher t
WHERE u.UserCode = g.GuardianCode
AND u.StudentCode = s.STUDENTCODE
AND t.teachercode = u.usercode
AND (
YEAR(u.DateTime) = '2013'
AND MONTH(u.DateTime) = '09'
)
AND u.RecordStatus = 'N'
AND c.classcode = s.classcode
ORDER BY u.datetime DESC
Please help me out

Answer 1

Try this with using CASE and i have joined you tables using LEFT join so there can be duplicates i have use GROUP BY also by u.id but bit confused for right column name please put the right column in group by
SELECT
u.ID,
u.StudentCode,
c.classname,
s.STUDENTNAME,
u.UserCode,
(CASE
WHEN u.usercode = t.teachercode THEN t.teachername
WHEN u.usercode = g.guardiancode THEN g.ForeName
ELSE END ) AS MessageSentBy,
u.Message,
u.ForTchrSname AS MessageSentTo,
DATE_FORMAT(u.datetime, '%d-%m-%y') AS datesent,
u.RecordStatus
FROM
tblupdates u
LEFT JOIN tblguardian g ON (u.UserCode = g.GuardianCode )
LEFT JOIN tblstudent s ON (u.StudentCode = s.STUDENTCODE )
LEFT JOIN tblclass c ON (c.classcode = s.classcode )
LEFT JOIN tblteacher t ON (t.teachercode = u.usercode)
WHERE u.RecordStatus = 'N'
AND (
YEAR(u.DateTime) = '2013'
AND MONTH(u.DateTime) = '09'
)
GROUP BY u.id
ORDER BY u.datetime DESC