+=item concat_sql [ DRIVER_NAME ] ITEMS_ARRAYREF
+
+Returns the items concatenated based on database type, using "CONCAT()" for
+mysql and " || " for Pg and other databases.
+
+You can pass an optional driver name such as "Pg", "mysql" or
+$dbh->{Driver}->{Name} to return a function for that database instead of
+the current database.
+
+=cut
+
+sub concat_sql {
+ my $driver = ref($_[0]) ? driver_name : shift;
+ my $items = shift;
+
+ if ( $driver =~ /^mysql/i ) {
+ 'CONCAT('. join(',', @$items). ')';
+ } else {
+ join('||', @$items);
+ }
+
+}
+
+=item midnight_sql DATE
+
+Returns an SQL expression to convert DATE (a unix timestamp) to midnight
+on that day in the system timezone, using the default driver name.
+
+=cut
+
+sub midnight_sql {
+ my $driver = driver_name;
+ my $expr = shift;
+ if ( $driver =~ /^mysql/i ) {
+ "UNIX_TIMESTAMP(DATE(FROM_UNIXTIME($expr)))";
+ }
+ else {
+ "EXTRACT( EPOCH FROM DATE(TO_TIMESTAMP($expr)) )";
+ }
+}
+