SQL to convert multiple rows into a single row of variable length

PHP Snippet 1:

SELECT
    FIELDS.NAME AS PROPERTYNAME,
    CASE WHEN PARAMS.NUMVAL IS NULL THEN STRINGVAL ELSE CAST(PARAMS.NUMVAL AS VARCHAR(100)) END AS PROPERTYVALUE
FROM
    PARAMS, FIELDS
WHERE
    PARAMS.FID = FIELDS.FID
        AND
    PARAMS.LID = 1
ORDER BY
    PARAMS.FID

PHP Snippet 2:

SELECT p.l_id, 
   GROUP_CONCAT(
       CONCAT(f.name,'=', 
          CASE WHEN p.stringval IS NULL
               THEN p.numval 
            ELSE p.stringval 
          END
       ) SEPARATOR '||'
   ) AS vals 
 FROM
    params AS p 
 LEFT JOIN fields AS f 
    ON  p.f_id=f.f_id 
 WHERE 
    p.l_id=1 
 GROUP BY 
    p.l_id;

PHP Snippet 3:

+------+---------------------------------------------------------- ... -+
| l_id | vals                                                           |
+------+---------------------------------------------------------- ... -+
|    1 | kv=50||ma=50||pressure=0||temp_ccd=-58||temp_sample=150|| ...  |
+------+---------------------------------------------------------  ...  +