Block selection mode is provided in QueryTool's SQL editor to aid in making multiple additions, changes or deletions to a block of SQL spanning multiple rows.
The Alt+Left mouse button drag or Alt+Shft+Arrow key within the SQL editor window activates block selection mode and enables the use of the mouse or arrow keys to highlight a block of columns and rows for selection. Once a block is highlighted, the keyboard can be used to delete, edit or insert text in the block. A Left mouse button click deactivates block selection mode.
Go to the Tools->QueryTool->SQL Editor Window section of the Help contents for more information on using the SQL editor.