MySQL select statement with CASE or IF ELSEIF? Not sure how to get the result

Another way of doing this is using nested IF statements. Suppose you have companies table and you want to count number of records in it. A sample query would be something like this

SELECT IF(
      count(*) > 15,
      'good',
      IF(
          count(*) > 10,
          'average',
          'poor'
        ) 
      ) as data_count 
      FROM companies

Here second IF condition works when the first IF condition fails. So Sample Syntax of the IF statement would be IF ( CONDITION, THEN, ELSE). Hope it helps someone.

Try this query -

SELECT 
  t2.company_name,
  t2.expose_new,
  t2.expose_used,
  t1.title,
  t1.seller,
  t1.status,
  CASE status
      WHEN 'New' THEN t2.expose_new
      WHEN 'Used' THEN t2.expose_used
      ELSE NULL
  END as 'expose'
FROM
  `products` t1
JOIN manufacturers t2
  ON
    t2.id = t1.seller
WHERE
  t1.seller = 4238

Syntax:

CASE value WHEN [compare_value] THEN result 
[WHEN [compare_value] THEN result ...] 
[ELSE result] 
END

Alternative: CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...]

mysql> SELECT CASE  WHEN 2>3 THEN 'this is true' ELSE 'this is false' END; 
+-------------------------------------------------------------+
| CASE  WHEN 2>3 THEN 'this is true' ELSE 'this is false' END |
+-------------------------------------------------------------+
| this is false                                               | 
+-------------------------------------------------------------+

I am use:

SELECT  act.*,
    CASE 
        WHEN (lises.session_date IS NOT NULL AND ses.session_date IS NULL) THEN lises.location_id
        WHEN (lises.session_date IS NULL AND ses.session_date IS NOT NULL) THEN ses.location_id
        WHEN (lises.session_date IS NOT NULL AND ses.session_date IS NOT NULL AND lises.session_date>ses.session_date) THEN ses.location_id
        WHEN (lises.session_date IS NOT NULL AND ses.session_date IS NOT NULL AND lises.session_date<ses.session_date) THEN lises.location_id
    END AS location_id
FROM activity AS act
LEFT JOIN li_sessions AS lises ON lises.activity_id = act.id AND  lises.session_date >= now()
LEFT JOIN session AS ses ON  ses.activity_id = act.id AND  ses.session_date >= now()
WHERE act.id