VERIFIED SOLUTION i

Identifying duplicate values in a column of data in MapInfo Pro using Sql Select

Products affected: MapInfo Pro™
 
With the table to query for duplicate values opened in MapInfo Pro, launch the SQL Select dialog.
MapInfo Pro 64-bit: Table > Selection > SQL Select
MapInfo Pro 32-bit: Query > SQL Select

At the select columns section of the dialog, remove the * and use the columns drop-down to select
the column that has duplicate values.
(The asterisk (*) is a wildcard indicating that all columns will be returned in the query.)
Click the "aggregate" drop-down and select "Count".
At the "Group By" section, use the "Columns" drop-down to select the same column from above that has duplicate values for some records.
For the "Sort By" section, manually enter "Col2" (without quotes), as the Count variable is the 2nd field selected at the Select Columns.

Run the query and any record that has a value greater than 1 for "Col2" has duplicate
values for that chosen field.

Sorting by col2 yields a query table sorted on the Count field to make it easier to find the records with duplicate values...
See screenshot example where the uscty153 table (found in the Introductory Data for MapInfo Pro) was used to find the States containing multiple points.
User-added image
If the table has entire records that are duplicated, users can use the MapInfo Pro tool called "Delete Duplicates" to delete the dupes and retain map objects....

 
UPDATED:  May 23, 2019