LineString(pt1,pt2,...)

Constructs a WKB LineString value from a number of WKB Point arguments.
If any argument is not a WKB Point, the return value is NULL. If the
number of Point arguments is less than two, the return value is NULL.

URL: http://dev.mysql.com/doc/refman/5.1/en/creating-spatial-values.html#gis-mysql-specific-functions

