#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?<!\.)\bmyTable\b"
Local $sString = "val changeMe= "select myTable.x,myTable.y,myTable.myTable from myTable join myTable2 ON myTable.x = myTable2.x" "
Local $sSubst = "myTable3"
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