MySQL Tutorial/Aggregate Functions/GROUP CONCAT
GROUP_CONCAT(expr) returns a string result with the concatenated non-NULL values from a group
The full syntax is as follows:
<source lang="sql">
GROUP_CONCAT([DISTINCT] expr [,expr ...]
[ORDER BY {unsigned_integer | col_name | expr} [ASC | DESC] [,col_name ...]] [SEPARATOR str_val])</source>