+=item group_concat_sql COLUMN, DELIMITER
+
+Returns an SQL expression to concatenate an aggregate column, using
+GROUP_CONCAT() for mysql and array_to_string() and array_agg() for Pg.
+
+=cut
+
+sub group_concat_sql {
+ my ($col, $delim) = @_;
+ $delim = dbh->quote($delim);
+ if ( driver_name() =~ /^mysql/i ) {
+ # DISTINCT(foo) is valid as $col
+ return "GROUP_CONCAT($col SEPARATOR $delim)";
+ } else {
+ return "array_to_string(array_agg($col), $delim)";
+ }
+}
+