How to compare data from two tables in sql? - mysql

Question

I have table like this:
table's name: registrationdate
I want to get the maximum value on last_update's column, so I use this query:
SELECT idtemp, max(last_update) FROM `registrationdate`
then the result will be like this:
and I have table like this:
table's name: temp
then I want to compare max(last_update) in registrationdate's table and generatedtime in temp's table
this is the schema:
what may I do so that I can get table like that? Thanks in advance.
Fyi, idtemp in registrationdate's table = id in temp's table

Answer 1

Please try the following...
SELECT ID AS ID,
generatedTime AS generatedTime,
tempTable AS tempTable,
CASE
WHEN generatedTime < maxLastUpdate THEN
'not'
ELSE
'update'
END AS UPDATEorNot
FROM temp
JOIN ( SELECT idtemp AS idtemp,
MAX( last_update ) AS maxLastUpdate
FROM registrationdate
GROUP BY idtemp
) AS maxLastUpdateFinder ON temp.ID = maxLastUpdateFinder.idtemp;
Assumptions
That records in temp that do not have at least one matching record in registrationdate do not need to be included in the output.
That the comparison and sample data are valid and the sample output's UPDATEorNot field should read not.
Explanation
This statement starts with a subquery that finds each unique value of idtemp in registrationdate and the most recent value of last_update associated with it.
An INNER JOIN is then performed between temp and the results of the subquery so that each record in temp with at least one corresponding record in registrationdate is retained and has its corresponding most recent value of last_update appended to it.
The fields from temp are then SELECTed, and a CASE statement used to determine the value to be selected for each record's UPDATEorNot field.
Please note that my statement will return not when the comparison that you supplied is applied to the sample data. If you want update to be chosen then you will need to change your comparison from generatedTime < max( last_update ) to generatedTime > max( last_update ), or to correct your sample data.
Testing
My statement was tested against a sample database created using the following script...
CREATE TABLE registrationdate
(
last_update DATETIME,
idtemp INT
);
INSERT INTO registrationdate ( last_update,
idtemp )
VALUES ( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 ),
( '2017-05-12 14:20:58', 0 );
CREATE TABLE temp
(
ID INT,
generatedTime DATETIME,
tempTable VARCHAR( 50 )
);
INSERT INTO temp ( ID,
generatedTime,
tempTable )
VALUES ( 0, '2017-05-01 14:37:00', 'temp_pelamardoktorjk' ),
( 2, '2017-05-01 14:37:00', 'temp_pelamarmagisteripk' ),
( 3, '2017-05-01 14:38:00', 'temp_pelamarmagisterstatusinstitusi' ),
( 4, '2017-05-01 14:38:00', 'temp_pelamarmagisterusia' ),
( 5, '2017-05-01 14:38:00', 'temp_pelamarmagisterstatusinstansi' );
If you have any questions or comments, then please feel free to post a Comment accordingly.
Appendix 1
The following is an alternative form of the above statement...
SELECT ID AS ID,
generatedTime AS generatedTime,
tempTable AS tempTable,
CASE
WHEN generatedTime < MAX( last_update ) THEN
'not'
ELSE
'update'
END AS UPDATEorNot
FROM temp
JOIN registrationdate ON temp.ID = registrationdate.idtemp
GROUP BY ID,
generatedTime,
tempTable;
Appendix 2
Please try the following attempted rewrite of the linked to code...
SELECT
generatedTime AS generatedTime,
tempTable AS tempTable,
CASE
WHEN ( ( generatedTime < ( SELECT MAX( last_update ) AS maxPelamarmhsdoktor
FROM pelamarmhsdoktor ) ) OR
( generatedTime < ( SELECT MAX( last_update ) AS maxAkdmstmayor
FROM akdmst_mayor ) ) OR
( generatedTime < ( SELECT MAX( last_update ) AS maxIpbmstdepartemen
FROM ipbmst_departemen ) ) OR
( generatedTime < ( SELECT MAX( last_update ) AS maxIpbmstfakultas
FROM ipbmst_fakultas ) ) OR
( generatedTime < ( SELECT MAX( last_update ) AS maxIpbrefjeniskelamin
FROM ipbref_jeniskelamin ) ) OR
( generatedTime < ( SELECT MAX( last_update ) AS maxJenisinstansi
FROM jenisinstansi ) ) OR
( generatedTime < ( SELECT MAX( last_update ) AS maxJenisinstitusi
FROM jenisinstitusi
) ) ) THEN
'Yes'
ELSE
'No'
END AS NeedsToUpdateOrNot
FROM generatedTime;