When I append arrays in google spreadsheets, all of the resulting elements are not rendered in cells. For example, if I enter the formula:
={{1,2,3}, {4,5,6
It is possible to make a union in Google Spreadsheet very easily. For example:
={'Sheet1'!A2:A;'Sheet2'!A2:A;'Sheet3'!A2:A}
See more info in Google Docs Help: Using arrays in Google Sheets