No, I was suggesting that you need to convert the report to use the command instead of all of your linked tables. I guess you could insert an unlinked subreport that does this, as long as your query provided the correct dataset. What you should NOT do, is add a command to a report that is already using tables (except if it is used just to populate a parameter picklist), as any linking would occur locally, and be very slow.
To convert to a command only as your datasource, you would do the following:
If you want to use your existing report design, you can create the union all query by copying your query into the add command area (adding your Det1DateCode field as the first field), adding "Union all" and then pasting it again, changing Det1DateCode to Det2DateCode in the second half of the query, like this:
SELECT `Summary`.`Det1DateCode` as DateCode,`Summary`.`Project`, `Summary`.`JobNumber`, `Fixed_Project_Details`.`Client`, `Fixed_Project_Details`.`Location`, `Summary`.`TrackerDate`, `Summary`.`DrillerName`, `Summary`.`Helper_1`, `Summary`.`Helper_2`, `Summary`.`RigNumber`, `Summary`.`Buggy_1`, `Summary`.`Buggy_2`, `Summary`.`Line/ShotPoint`, `Summary`.`Re-Drill`, `Summary`.`Backup`, `Summary`.`Det1Resistance`, `Summary`.`Det2Resistance`, `Summary`.`HoleDepth`, `Summary`.`TopofCharge`, `Summary`.`Lithology_1`, `Summary`.`Lithology_2`, `Summary`.`ShooterCaution`, `Summary`.`TrackerTime`, `Fixed_Project_Details`.`DetonatorLength`, `Summary`.`ChargeWeight_1`, `Summary`.`ChargeWeight_2`, `Summary`.`ChargeWeight_3`
FROM `Fixed Project Details` `Fixed_Project_Details` INNER JOIN `Summary` `Summary` ON (`Fixed_Project_Details`.`Project`=`Summary`.`Project`) AND (`Fixed_Project_Details`.`JobNumber`=`Summary`.`JobNumber`)
Union All
SELECT `Summary`.`Det2DateCode` as DateCode,`Summary`.`Project`, `Summary`.`JobNumber`, `Fixed_Project_Details`.`Client`, `Fixed_Project_Details`.`Location`, `Summary`.`TrackerDate`, `Summary`.`DrillerName`, `Summary`.`Helper_1`, `Summary`.`Helper_2`, `Summary`.`RigNumber`, `Summary`.`Buggy_1`, `Summary`.`Buggy_2`, `Summary`.`Line/ShotPoint`, `Summary`.`Re-Drill`, `Summary`.`Backup`, `Summary`.`Det1Resistance`, `Summary`.`Det2Resistance`, `Summary`.`HoleDepth`, `Summary`.`TopofCharge`, `Summary`.`Lithology_1`, `Summary`.`Lithology_2`, `Summary`.`ShooterCaution`, `Summary`.`TrackerTime`, `Fixed_Project_Details`.`DetonatorLength`, `Summary`.`ChargeWeight_1`, `Summary`.`ChargeWeight_2`, `Summary`.`ChargeWeight_3`
FROM `Fixed Project Details` `Fixed_Project_Details` INNER JOIN `Summary` `Summary` ON (`Fixed_Project_Details`.`Project`=`Summary`.`Project`) AND (`Fixed_Project_Details`.`JobNumber`=`Summary`.`JobNumber`)
Then do not link the command to anything (ignore the message). Then replace all fields in the report with the corresponding command fields, including in formulas, sort areas, selection formulas, and groups. Once you no longer see any references to tables in the field explorer, you can remove them in the database expert. This assumes that your current query selects the records you want, i.e., that all criteria in your selection formula pass to the SQL. If you have selection criteria that are not appearing in the Query, you need to build them in, since you will no longer be using the select expert in the main report.
-LB