SELECT topics.*, count(messages.text) as count, messages.nik FROM `messages` right JOIN `topics` ON messages.parent=topics.key GROUP BY topics.key, topics.datetime 

SELECT topics . * , count( messages.text ) AS count, SUBSTR( min( CONCAT( messages.datetime, messages.nik ) ) , 20 ) 
FROM `messages` 
RIGHT JOIN `topics` ON messages.parent = topics.key
GROUP BY topics.key, topics.datetime
LIMIT 0 , 30

SELECT * FROM topics right JOIN messages ON messages.parent = topics.key as t1, (SELECT max(CHAR_LENGTH(topics.title)) FROM topics) as t2

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'as t1, (SELECT max(CHAR_LENGTH(topics.title)) FROM topics) as t2' at line 1

SELECT * FROM topics right JOIN messages ON messages.parent = topics.key

SELECT * FROM topics as t1, (SELECT max(CHAR_LENGTH(topics.title)) FROM topics) as t2

SELECT
	topics.nik,
	topics.datetime,
	topics.title,
	count( messages2.text ) count,
	SUBSTR( max( CONCAT( messages2.datetime, messages2.nik ) ) , 20 ) lastnik
FROM `topics`
JOIN `messages` ON messages.parent = topics.key
	AND messages.nik = 'Admin'
JOIN `messages` as messages2 ON messages2.parent = topics.key
GROUP BY topics.key
ORDER BY topics.datetime DESC 
LIMIT 40

select
	( select
		count( messages2.text )
	from `messages` as messages2 where messages2.parent = zz.key) count,
	( select
		SUBSTR( max( CONCAT( messages2.datetime, messages2.nik ) ) , 20 )
	from `messages` as messages2 where messages2.parent = zz.key) lastnik,
	zz.*
FROM 
(
SELECT
	topics.key,
	t2.lentitle,
	topics.nik ts,
	topics.datetime topicdate,
	topics.title
FROM `topics`
JOIN `messages` ON messages.parent = topics.key
	AND messages.nik = 'Admin',
(
	SELECT max( CHAR_LENGTH( title ) ) lentitle
	FROM topics
) AS t2
GROUP BY topics.key
ORDER BY topics.datetime DESC 
LIMIT 40)zz

select
	( select
		count( messages2.text )
	from `messages` as messages2 where messages2.parent = zz.key) count,
	( select
		SUBSTR( max( CONCAT( messages2.datetime, messages2.nik ) ) , 20 )
	from `messages` as messages2 where messages2.parent = zz.key) lastnik,
	zz.*
FROM 
(
SELECT
	topics.key,
	t2.lentitle,
	topics.nik ts,
	topics.datetime topicdate,
	topics.title
FROM `topics`
JOIN `messages` ON messages.parent = topics.key
	AND messages.nik = 'Admin',
(
	SELECT max( CHAR_LENGTH( title ) ) lentitle
	FROM topics JOIN `messages` ON messages.parent = topics.key
	AND messages.nik = 'Admin'
) AS t2
GROUP BY topics.key
ORDER BY topics.datetime DESC 
LIMIT 40)zz

SELECT *
FROM topics
JOIN messages ON
 messages.parent = topics.key
 AND messages.nik = 'Admin'

max( CHAR_LENGTH( title ) ) lentitle 

SELECT table.text 
FROM table 

max( CHAR_LENGTH( table.text ) ) 

set @max=0;
select *, @max:=IF(tmp.lentitle>@max, tmp.lentitle, @max) as maxlentitle from (
	SELECT
		*,
		CHAR_LENGTH(topics.title) as lentitle,
		(SELECT CONCAT( count( text ), '	', max( CONCAT( datetime, '	', nik ) ) ) 
			FROM messages
			WHERE parent = topics.key
		)count_lastnik
	FROM topics
	where topics.key in
		(SELECT parent
			FROM messages
			WHERE messages.nik = 'Admin'
			GROUP BY parent
		)
) as tmp

SELECT *,
	( select datetime
	from messages where messages.parent = topics.key)
FROM topics
LIMIT 10

SELECT *,
	( select max(datetime) from messages where messages.parent = topics.key)
FROM (select * from topics LIMIT 10) as topics

SELECT *,
	( select max(datetime) from messages where messages.parent = topics.key)
FROM topics
LIMIT 10

#1
select (select datetime from topics where topics.key = p.parent) datetime
from ( SELECT parent FROM messages GROUP BY parent ) p
#2
SELECT datetime
FROM topics
where topics.key in	( SELECT parent FROM messages ) # GROUP BY parent???
#3
SELECT topics.datetime
FROM topics
JOIN messages ON topics.key = messages.parent
GROUP BY datetime

EXPLAIN SELECT distinct topics.*
FROM topics join messages
ON topics.key = messages.parent Where messages.nik = 'ss'