I suspect you want to keep the incidents file as an excel file (to continue monitoring)? Probably the most straightforward way to do this would be to use Excel lookup functions to create geometry in the Excel file, which can then be used for mapping directly.
- Add X and Y colums to the geometry point file, and save-as a CSV file;
- Open the CSV in Excel and copy it as a new tab ('locations') into your Excel file;
- Add X and Y columns to the original Excel Incidents tab, and use a lookup function to get the X and Y values from the locations tab;
- Map incidents directly in Arc (or QGIS using the XY plugin) by reading the Excel file.
Add X and Y columns to your point SDE layer (I don't use ArcGIS but there are instructions here). Export the attribute table to a CSV file and open in Excel:
Schools point table:
id_school X Y
1 32.1 -2.3
2 33.0 -2.4
3 32.0 -2.0
Add it as a tab to your 'incident' Excel file; the 'incidents' might look like:
id_school Incident Date
1 A 2014-04-01
1 B 2014-04-02
2 A 2014-04-01
3 B 2014-04-11
Add an X and Y column to the incident tab, and use the vlookup function to add the values to those columns, using the format
vlookup(id_school, points_tab_range, column number):
id_school Incident Date X
1 A 2014-04-01 =vlookup(A2, points!A1:C5, 2)
The X column would then be populated with the value 32.1. Do the same for the Y column but with column 3 indicated. If you update schools or locations, add them to the lookup range.
You can then add the Excel file as a layer in ArcGIS; if using QGIS, the 'XY Tools' plugin will read .XLS (not .XLSX unfortunately) in the same way.