Find difference in 2 tables / recordsets MySQL - mysql

Question

I have 2 tables in MySQL DB (A and B)
Both have very similar structure since table B has records that are inserted with all data each time user changes his data in table A to have full history of changes. Column Lastupdate is INT type and keeps time of update in UNIX timestamp format
So let’s say tables have records like that:
TableA
Id User_id Name1 Name2 Lastname Lastupdate
1 12 John Alexander Smith 1405594757
2 27 Marry Ann Poppins 1405594877
3 51 Jean Claude VanFist 1405594677
Table B
Id User_id Name1 Name2 Lastname Lastupdate
1 12 John Alexander Smit 1405594747
2 27 Marry Ann Poppins 1405594757
3 51 Jean Claude VanFist 1405594757
1 12 John 1405594727
1 12 John Alex 1405594737
3 51 Jean VanFist 1405594757
For each record from table A I would like to see comparison with the most current record of table B (basing on Lastupdate) with the information which field was changed
So for user_id = 12 I would have something like
Id User_id Name1 Name2 Lastname Lastupdate
1 12 John Changed name2:Alexander Changed lastname:Smith 1405594757
I was trying something like that
SELECT if(u1.name1 <> u2.name1, CONCAT("Changed: ",u1.name1), u1.name1)
FROM tableA u1,tableB u2
WHERE u1.user_id = 7433 AND u2.user_id = 7433
But it seems not to be right way please advise

Answer 1

This should indicate what field values changed as well as what they were and what they became:
select a.user_id,
case when a.name1 <> b.name1 then concat(b.name1,' changed to ',a.name1) else null end as name1_chg,
case when a.name2 <> b.name2 then concat(b.name2,' changed to ',a.name2) else null end as name2_chg,
case when a.lastname <> b.lastname then concat(b.lastname,' changed to ',a.lastname) else null end as lastname_chg
from tablea a
join tableb b
on a.user_id = b.user_id
where b.lastupdate = (select max(x.lastupdate)
from tableb x
where x.lastupdate < a.lastupdate and x.user_id = a.user_id)