¿Valores de columna dividida de MySQL para usar en la subconsulta?

No es una buena idea mantener los datos de esta manera.

La primera idea que se me ocurre es:http://sqlfiddle.com/#!2/ 1dd77/4

SELECT b.*, GROUP_CONCAT(a.name SEPARATOR ':')
FROM table2 as b
LEFT JOIN table1 as a
on b.var = a.id 
  OR  b.var regexp(CONCAT('^',a.id,':'))
  OR  b.var regexp(CONCAT(':',a.id,':'))
  OR  b.var regexp(CONCAT(':',a.id,'$'))
 GROUP BY b.id

EDITAR 1

Variante ordenada:http://sqlfiddle.com/#!2/1dd77/38

SELECT b.*, GROUP_CONCAT(a.name ORDER BY FIND_IN_SET(a.id, REPLACE(b.var,":",",")) SEPARATOR ':' )
FROM table2 as b
LEFT JOIN table1 as a
on b.var = a.id 
  OR  b.var regexp(CONCAT('^',a.id,':'))
  OR  b.var regexp(CONCAT(':',a.id,':'))
  OR  b.var regexp(CONCAT(':',a.id,'$'))
 GROUP BY b.id