mysql selecting data from two tables

Dear Experts,
I use PHP and MySql,
I need to select the max mounth data from table1 however, I already have a left join.
I confused, How can I do that?


SELECT table1.bk,table1.nk,table1.ay, table2.isim
FROM table1
LEFT JOIN table2 ON table1.bk = table2.uid
[b]WHERE mounth =  '(I'd likte to select the max(mounth data of the table1 where yil='2018')' [/b]
GROUP BY bk

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BRMarketingAsked:
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Ryan ChongCommented:
max of table1.mounth i guess? then try:

SELECT table1.bk, table1.nk, table1.ay, table2.isim
FROM (select max(mounth) mounth from table1 where yil='2018' ) table1
LEFT JOIN table2 ON table1.bk = table2.uid
WHERE table2.mounth =  table1.mounth
GROUP BY table1.bk, table1.nk, table1.ay, table2.isim

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Ryan ChongCommented:
some amendment to the code:

SELECT table1.bk, table1b.nk, table1b.ay, table2.isim
FROM (select max(mounth) mounth from table1 where yil='2018' ) table1
LEFT JOIN table1 table1b ON table1.bk = table1b.bk
LEFT JOIN table2 ON table1.bk = table2.uid
WHERE table2.mounth =  table1.mounth
GROUP BY table1.bk, table1b.nk, table1b.ay, table2.isim

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BRMarketingAuthor Commented:
there is an error message:
#1066 - Not unique table/alias: 'table1b'
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Ryan ChongCommented:
what if trying this? sorry that don't have the MySQL in my working environment to test now.

SELECT table0.bk, table1.nk, table1.ay, table2.isim
FROM (select max(mounth) mounth from table1 where yil='2018' ) table0
LEFT JOIN table1 ON table0.bk = table1.bk
LEFT JOIN table2 ON table0.bk = table2.uid
WHERE table2.mounth =  table1.mounth
GROUP BY table0.bk, table1.nk, table1.ay, table2.isim

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BRMarketingAuthor Commented:
I think we will get the same error. Because there is no table with the name table0 and we did not define it as alias.
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Ryan ChongCommented:
try this:

SELECT table1.bk, table1.nk, table1.ay, table2.isim
FROM (select max(mounth) mounth from table1 where yil='2018' ) as table0
LEFT JOIN table1 ON table0.mounth = table1.mounth
LEFT JOIN table2 ON table1.bk = table2.uid
WHERE table2.mounth =  table1.mounth
GROUP BY table1.bk, table1.nk, table1.ay, table2.isim

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BRMarketingAuthor Commented:
that is perfect.
thank you very much
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Olaf DoschkeSoftware DeveloperCommented:
You mean month? Is that stored in a column named table1.month? Or part of a date column? What's the table1 column named, of which you can get the month, you only gave a yil field containing year (as string?) It's recommendable to store dates in the form of data type date and use functions like year() and month()

A join doesn't hinder you at all to fetch only latest month data.

Creating sample data
Create Table table1 
   (id int AUTO_INCREMENT, t1_data char(10), date_entered date, PRIMARY KEY (id));
Create Table table2 
   (id int AUTO_INCREMENT, table1id int, t2_data char(10), PRIMARY KEY (id));

Insert Into table1 (t1_data, date_entered) Values ('testing','2018-01-04');
Insert Into table1 (t1_data, date_entered) Values ('hello,','2018-02-01');
Insert Into table1 (t1_data, date_entered) Values ('world!','2018-02-10');

Insert Into table2 (table1id, t2_data) Values (1,'x');
Insert Into table2 (table1id, t2_data) Values (2,'y');
Insert Into table2 (table1id, t2_data) Values (3,'z');

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notice t1_data, and t2_data as placeholders for all other data colums you have in these tables.

Querying max month data of table1 joined to table2:
Select t1.id as t1id, t2_data, t1.date_entered, t2_data From table1 as t1
Inner join table2 as t2 on t2.table1id = t1.id
Inner join (select max(date_entered) as maxdate from table1) as the on 1=1
Where year(t1.date_entered)=year(the.maxdate) 
and month(t1.date_entered)=month(the.maxdate)

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Also see http://sqlfiddle.com/#!9/1ab791/2

Bye, Olaf.
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BRMarketingAuthor Commented:
Dear Olaf,
thank you very much for your comment. I find all your comments very helpful. I learned a lot from you. Best regards.
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