Question

I have little problem with mysql query. I need something like GROUP_CONCAT in GROUP_CONCAT. LOOK:

Database design :

SELECT cid, country, capital,
    GROUP_CONCAT(DISTINCT mid, '=',city SEPARATOR '|*|') AS data
FROM t1
    INNER JOIN t2 ON t2.c_id = t1.cid
    INNER JOIN t3 ON t2.c_id = t3.mid
WHERE t1.cid =1

Return

[cid] => 1
[country] => France
[capital] => Paris
[data] => 1=Lyon|*|2=Chartres|*|3=Valence

But I want join to this query table t4 (I haven’t idea how to do this) and it will be good if output will be looks like this

[cid] => 1
[country] => France
[capital] => Paris
[data] => 1=Lyon=|*|2=Chartres=Max#Alex#Frank|*|3=Valence=John

ps.
t4.m_id = t3.mid

Answer 1

I am not exactly sure why you would want to do this in SQL, but here is a version that returns the desired result:

SELECT  t1.cid,
  t1.country,
  t1.capital,
  GROUP_CONCAT(DISTINCT t34.mid,"=", t34.city, "=", t34.names ORDER BY t34.mid SEPARATOR "|*|" )AS data
FROM table1 t1
INNER JOIN table2 t2 
  ON t1.cid = t2.c_id
LEFT JOIN
(
  select t3.mid, t3.city,
    Coalesce(GROUP_CONCAT(DISTINCT t4.names SEPARATOR "#"), '') names
  from table3 t3
  left join table4 t4
    on t3.mid= t4.m_id
  group by t3.mid, t3.city
) t34
  ON t2.city_id = t34.mid
where t1.cid = 1
group by t1.cid, t1.country

See SQL Fiddle with Demo

Result:

| CID | COUNTRY | CAPITAL |                                                DATA |
---------------------------------------------------------------------------------
|   1 |  France |   Paris | 1=Lyon=|*|2=Chartes=Max#Alex#Frank|*|3=Valence=John |