Compare worksheets within a Workbook

There's no built in utility to do what you're asking. There are script extensions available to compare two different files, but that's a bit of a different function than comparing two sheets within the same workbook.

Suggestion: Create two different DDT.ExcelDriver objects, one for each sheet.  Build a while loop that loops both sheets, comparing column values as desired.  It would be something like:

var sheet1Driver = DDT.ExcelDriver('C:\\MyFile.xls', 'Sheet1', true);
var sheet2Driver = DDT.ExcelDriver('C:\\MyFile.xls', 'Sheet2', true);

while ((!sheet1Driver.EOF()) && (!sheet2Driver.EOF()){
   //Do your comparison stuff
   sheet1Driver.Next();
   sheet2Driver.Next();

}

Test Complete provides several different ways to pull in data from excel files:

https://support.smartbear.com/testcomplete/docs/testing-with/advanced/working-with-external-data-sources/excel/index.html?q=excel