How can I merge multiple tabs in a Google Spreadsheet using Google App Script?

Question

How can I merge multiple tabs in a Google Spreadsheet using Google App Script ? Data in all the tabs keep changing.

For example, I have 'Sheet1', 'Sheet2' and 'Sheet3' in a Google spreadsheet. Data in all these sheets have 3 columns - Name and email ID & Region. Now, I want to merge/combine the data present in these 3 sheets/tabs into a 4th Sheet i.e. 'Sheet 4' having same Columns (name, email Id & Region). The 4th sheet should have data as - data of Sheet1 followed by Sheet2 and then Sheet3. The number of rows in all the 3 sheets keeps changing.

Answer 1

=query({Sheet1!A1:C; Sheet2!A1:C; Sheet3!A1:C}, "where Col1 is not null", 0)

I wouldn't use a script for this; the worksheet formulas are much faster, at least most of the time. Make sure you use semicolons to separate the ranges. Semicolons are the End_Of_Row operator for array literals.

If you really want to use a script...

function combineSheets() {
  var sApp = SpreadsheetApp.getActiveSpreadsheet();
  var s1= sApp.getSheetByName("Sheet1");
  var s2= sApp.getSheetByName("Sheet2");
  var s3= sApp.getSheetByName("Sheet3");
  var s4= sApp.getSheetByName("Sheet4");
  //  If Sheet4 doesn't exist you'll need to create it here.
  
  var s1values = s1.getRange(1,1,s1.getLastRow(),3).getValues();
  var s2values = s2.getRange(1,1,s2.getLastRow(),3).getValues();
  var s3values = s3.getRange(1,1,s3.getLastRow(),3).getValues();
  
  //  Now, we can put out all together and stuff it in Sheet4
  var s4values = [];
  s4values =  s1values.concat(s2values,s3values);
  s4.getRange(1,1,s4values.length,3).setValues(s4values);
}