Question

Table

---------------------------------------------
| id | first_name | middle_name | last_name |
---------------------------------------------
| 1  | abc        |             | def       |
---------------------------------------------
| 2  |            |             | xyz       |
---------------------------------------------
| 3  |  xyz       |             |           |
---------------------------------------------          

I want sql query which gives output as fields name which contains values and exclude fields which has empty value or null value.

like

id,
first_name,
last_name

Answer 1

First try, see fiddle for result:

http://sqlfiddle.com/#!2/b6d7b/7

SELECT
  CONCAT_WS(',',
      IF(id          IS NULL, NULL, 'id'),
      IF(first_name  IS NULL, NULL, 'first_name'),
      IF(middle_name IS NULL, NULL, 'middle_name'),
      IF(last_name   IS NULL, NULL, 'last_name')
  )
FROM person

To my best knowledge you can’t create MySQL queries which uses dynamically created table/field names. The query optimizer has to exactly know before actual execution what tables and fields will be used in the query, that’s why the above query contains manually written field names.

While you can create queries about database columns using INFORMATION_SCHEMA, you can’t use the received column names for querying, unless if you generate the needed sql code with php code, stored procedure, etc.

See http://dev.mysql.com/doc/refman/5.0/en/columns-table.html

If you wanted to find persons with ‘joh’ in their names, and the field names actually containing ‘joh’, you could use a similar query:

http://sqlfiddle.com/#!2/f2597/3

SELECT
  id AS person_id,
  CONCAT_WS(',',
      IF(first_name  LIKE '%joh%', 'first_name'  , NULL),
      IF(middle_name LIKE '%joh%', 'middle_name' , NULL),
      IF(last_name   LIKE '%joh%', 'last_name'   , NULL)
  ) AS name_parts
FROM person
WHERE first_name  LIKE '%joh%'
   OR middle_name LIKE '%joh%'
   OR last_name   LIKE '%joh%';

If you want every column name, where there is at least one NOT NULL value in that column, then try this query:

http://sqlfiddle.com/#!2/8dec7/5

SELECT
  CONCAT_WS(',',
      IF(COUNT(id          )>0, 'id'         ,NULL),
      IF(COUNT(first_name  )>0, 'first_name' ,NULL),
      IF(COUNT(middle_name )>0, 'middle_name',NULL),
      IF(COUNT(last_name   )>0, 'last_name'  ,NULL)
  )
FROM person;

It uses COUNT( expr ), which ( http://dev.mysql.com/doc/refman/5.1/en/group-by-functions.html#function_count ) Returns a count of the number of non-NULL values of expr.