MySQL COALESCE() function

MySQL COALESCE() function returns the first non-NULL value of a list, or NULL if there are no non-NULL values.

MySQL Version : 5.6

Syntax

COALESCE(value1,value2,value3,...)

The above syntax is equivalent to the following IF-THEN-ELSE statement

  IF value1 is not NULL THEN
     result = value1;
  ELSIF value2 is not NULL THEN
     result = value2;
  ELSIF value3 is not NULL THEN
     result = value3;
  ELSE
     result = NULL;
  END IF; 

- See more at: http://www.w3resource.com/mysql/comparision-functions-and-operators/coalesce-function.php#sthash.mgOL7uGR.dpuf