用if语句连接另一个表

Question

I want to join another table if a field of current table equals to some specific value.
For example : ( this is not mysql syntax )

SELECT * FROM `products` ( IF products.is_package IS NOT NULL THEN INNER JOIN `packages` )  

Table products:

 +----+-----------+
 | id | is_package|
 +----+-----------+
 | 1  |   1       | // which joins package with id 1
 +----+-----------+
 | 2  | NULL      |
 +----+-----------+
 | 3  |   2       | // which joins package with id 2
 +----+-----------+

Is it possible to do this in mysql?

Answer 1

 SELECT * FROM `products` LEFT JOIN `packages` 
  ON products.is_package = packages.id

Answer 2

Your if condition you can just put it in WHERE clause .try this

  SELECT * FROM `products` LEFT JOIN `packages` 
  ON your_clause_here