Added the SaMPLE operator to the (only) file that exists for documenting the relational operators in the sql frontend.
Added the SaMPLE operator to the (only) file that exists for documenting the relational operators in the sql frontend.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb