Success for creating the desired
report! Thanks again to Kevin and Steven for their help. Here's the goal and then how I reached it. Maybe this will be helpful to

another newbie developing a
report that requires some complex string functions to prepare for the
report. I have a database with a table that several columns, but the relavant ones are: visitee, datevisited, visitor. I want a
report in which each line lists a visitee followed by a list of dates he/she was visited along with visitor(s) initials for each visit.
Report row example: John Doe 1/8/18:VVW,MVW-1/26/18:HH-1/14/18:TS
I ran into a problem trying Steven's suggestion which was to create #TABLE_ID# with select statement and then alter/update it successively until I had what I wanted for the
report. I could not figure out how to run the GROUP_CONCAT function doing an update to #TABLE_ID#. I think I would have the same issue using views. So I went in the direction of creating another table (temp_report), running several updates on it, and finally creating the table #TABLE_ID# for the
report using the new table. There may be better ways of doing this, but it works and I learned a lot about nubuilder doing this.
$a = "DROP TABLE IF EXISTS temp_report"; // Note1
nuRunQuery ($a);
$b = "SELECT * FROM databasetable WHERE [several criteria based on form object values]";
nuRunQuery ("CREATE TABLE temp_report AS $b");
$c = "ALTER TABLE temp_report ADD visitorinitials varchar(25), ADD datestromg varchar(25), ADD dateinitials varchar(25)";
nuRunQuery($c);
$d = "UPDATE temp_report SET visitorinitials = regex_replace('[^A-Z\,]','',visitor)"; //Note 2
nuRunQuery($d);
$e = "UPDATE temp_report SET datestring = Date_FORMAT(datevisited,'%c/%e/%y')"; //Note 3
nuRunQuery($e);
$f = "UPDATE temp_report SET dateinitials = CONCAT_WS(':',datestring,visitorinitials)";
nuRunQuery($f);
$g = "Create TABLE #TABLE_ID# AS SELECT visitee, GROUP_CONCAT(dateinitials SEPARATOR '-') as groupeddateinitials FROM temp_report GROUP BY visitee";
nuRunQuery($g);
Note 1: Remove the table so it can be rebuilt for the
report. Since I was creating and then updating a table, during development I could easily test each step of the process. (Comment out those steps after the step being tested, run the
report, ignore
report, but go to the database directly (Builder -> Database) and check the content of the temp_report table after that step.)
Note 2: See previous entry for note on regex_replace. Here it strips out everything but Uppercase letters and commas from a list of names.
Note 3 Convert the date to a sring with a short form (example: 1/1/19) to facilitate the next step.