How to group mysql rows with same column value into one row?

Use GROUP_CONCAT() like this:

 SELECT k.id, GROUP_CONCAT(d.value)
  FROM keywords AS k
  INNER JOIN data as d ON k.id = d.id
  GROUP BY k.id

Also, you may need to do ORDER BY d.name to get exact order of values as you want. Like this:

 SELECT k.id, GROUP_CONCAT(d.value ORDER BY d.name separator ' ')
  FROM keywords AS k
  INNER JOIN data as d ON k.id = d.id
  GROUP BY k.id