one of the documented procedures in this installation of the ACS
db_list   sql
What it does:
Returns a list containing the first column of each row returned by the SQL query $sql.
Defined in: /web/philip/packages/acs-core/10-database-procs.tcl

Source code:

    # Can't use db_foreach here, since we need to use the ns_set directly.
    db_with_handle db {
	set result [list]
	set selection [ns_db select $db $sql]
	while { [ns_db getrow $db $selection] } {
	    lappend result [ns_set value $selection 0]
    return $result