How to join table in SQL correctly? [duplicate] - mysql

Question

I am really confused with this codes. I have query like this
CREATE ALGORITHM=UNDEFINED DEFINER=`root`#`localhost` SQL SECURITY DEFINER VIEW `aIPK` AS select
`ipbmst_fakultas`.`Kode` AS `Fakultas`,
`ipbmst_departemen`.`Kode` AS `Departemen`,
`akdmst_mahasiswamagister`.`NIM` AS `NIM`,
`akdmst_mahasiswamagister`.`TahunMasuk` AS `TahunMasuk`,
`akdhis_kelanjutanstudi`.`IPK` AS `IPK`
from (((((`akdmst_mahasiswamagister` left join `akdmst_mayor` on((`akdmst_mahasiswamagister`.`MayorID` = `akdmst_mayor`.`ID`)))
left join `ipbmst_departemen` on((`akdmst_mayor`.`DepartemenID` = `ipbmst_departemen`.`ID`)))
left join `ipbmst_fakultas` on((`ipbmst_departemen`.`FakultasID` = `ipbmst_fakultas`.`ID`)))
left join `ipbmst_orang` on((`akdmst_mahasiswamagister`.`NIM` = `ipbmst_orang`.`NIMS2Key`)))
left join `akdhis_kelanjutanstudi` on((`akdhis_kelanjutanstudi`.`NIM` = `ipbmst_orang`.`NIMS2Key`)))
WHERE `akdhis_kelanjutanstudi`.`IPK` IS NOT NULL
order by NIM
LIMIT 100;
but "IPK" result is NULL, actually IPK has its value. What's wrong with those codes?
Here is my table structure:
table 1: akdmst_mahasiswamagister (ID, MahasiswaID, NIM, MayorID, TahunMasuk)
table 2: akdmst_mayor(ID, DepartemenID)
table 3: ipbmst_departemen(ID, FakultasID, DepartmenName)
table 4: ipbmst_fakultas(ID, FacultyName)
table 5: ipbmst_orang(ID, Name, NIMS2Key)
table 6: akdhis_kelanjutanstudi(ID, NIM, IPK)
I also have the other problem about this query. It took too much time to query the view. I thought maybe it's because table akdhis_kelanjutanstudi that consists of more than 300K data records. I have used "LIMIT 100" but still the same. could you please help me to solve that problem?

Answer 1

I don't know what the exact problem(s) is, but your WHERE clause has a problem:
WHERE IPK IS NOT NULL
It is not allowed to refer to a column alias in the WHERE clause, because its value may not be determined yet. Instead, you should use this:
WHERE akdhis_kelanjutanstudi.IPK IS NOT NULL
Update:
The parentheses you used in your original view look strange, unnecessary, and possibly wrong. Try using the following:
CREATE ALGORITHM=UNDEFINED DEFINER=`root`#`localhost`
SQL SECURITY DEFINER VIEW aIPK AS
SELECT t4.Kode AS Fakultas,
t3.Kode AS Departemen,
t1.NIM AS NIM,
t1.TahunMasuk AS TahunMasuk,
t6.IPK AS IPK
FROM akdmst_mahasiswamagister t1
LEFT JOIN akdmst_mayor t2
ON t1.MayorID = t2.ID
LEFT JOIN ipbmst_departemen t3
ON t2.DepartemenID = t3.ID
LEFT JOIN ipbmst_fakultason t4
ON t3.FakultasID = t4.ID
LEFT JOIN ipbmst_orang t5
ON t1.NIM = t5.NIMS2Key
LEFT JOIN akdhis_kelanjutanstudi t6
ON t6.NIM = t5.NIMS2Key
WHERE t6.IPK IS NOT NULL
ORDER BY NIM
LIMIT 100;

Answer 2

Running sql instead of creating algorithm is easier for testing.
In your case check the conditions in join
on((`akdhis_kelanjutanstudi`.`NIM` = `ipbmst_orang`.`NIMS2Key`)))
also you need to change
WHERE `akdhis_kelanjutanstudi`.`IPK` IS NOT NULL
To
WHERE `IPK` IS NOT NULL

Answer 3

you have mistake in your description,
your tables are
table 1: akdhis_mahasiswamagister (ID, MahasiswaID, NIM, MayorID, TahunMasuk)
table 2: akdmst_mayor(ID, DepartemenID)
table 3: ipbmst_departemen(ID, FakultasID, DepartmenName)
table 4: ipbmst_fakultas(ID, FacultyName)
table 5: ipbmst_orang(ID, Name, NIMS2Key)
table 6: akdhis_kelanjutanstudi(ID, NIM, IPK)
but i dont see "akdhis_mahasiswamagister" table in your select
CREATE ALGORITHM=UNDEFINED DEFINER=root#localhost SQL SECURITY DEFINER VIEW aIPK AS select
ipbmst_fakultas.Kode AS Fakultas,
ipbmst_departemen.Kode AS Departemen,
akdmst_mahasiswamagister.NIM AS NIM,
akdmst_mahasiswamagister.TahunMasuk AS TahunMasuk,
akdhis_kelanjutanstudi.IPK AS IPK
from (((((akdmst_mahasiswamagister inner join akdmst_mayor on((akdmst_mahasiswamagister.MayorID = akdmst_mayor.ID)))
inner join ipbmst_departemen on((akdmst_mayor.DepartemenID = ipbmst_departemen.ID)))
inner join ipbmst_fakultas on((ipbmst_departemen.FakultasID = ipbmst_fakultas.ID)))
inner join ipbmst_orang on((akdmst_mahasiswamagister.NIM = ipbmst_orang.NIMS2Key)))
inner join akdhis_kelanjutanstudi on((akdhis_kelanjutanstudi.NIM = ipbmst_orang.NIMS2Key)))
WHERE IPK IS NOT NULL
order by NIM
LIMIT 100;
akdhis_mahasiswamagister and akdmst_mahasiswamagister are different? may you are using wrong table, and so you have incorrect information