   CONCAT_WS(separator,str1,str2,...)

CONCAT_WS() stands for CONCAT With Separator and is a special form of
CONCAT().  The first argument is the separator for the rest of the
arguments.
The separator is added between the strings to be concatenated.
The separator can be a string as can the rest of the
arguments. If the separator is NULL, the result is NULL.
The function skips any NULL values after the
separator argument.
