#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "\bwhere(?:(?:(?!where)[^][])*\[[^][]*])+\s*"
Local $sString = "where this condition and [this = 1] group by 1,2,3" & @CRLF & _
"where that and that do that where [this = 1] and [that = 1] group by 1,2,3"
Local $sSubst = ""
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm