I am trying to debug an issue and trying to make sense of the log
as per example
it is obvious the first part is the date and time
then the second mysterious element  what is this? a process id somewhere? then how can I locate it (from which file/ object/ line etc?
the third one [15e590af-c6c8-457e-2731-4c0f0456dd5c] is the user id
the fourth one is the error/log level
and the query.
So my question how may I find out where this line is residing? what triggered that line?
how can I debug?
If you look at include/SugarLogger/SugarLogger.php line 197. It describes the format as
date [PHP’s process ID] [userID] [debug level] debug message.
I think you need to change the debug level to debug. In order to get a “clearer” picture.
To answer your question; you should search for “SELECT u1.first_name, u1.last_name from users u1, users u2” in your instance of SuiteCRM. There are different ways to achieve this. If you are using linux then you can opt for grep. If you have an Integrated Development Environment the you can use your find in files feature. If you are using windows. You can use the search files and folders option. Explorer has an advanced feature for searching the contents of the files.
I did a quick search for you and found in modules/Employees/Employee.php line 129 is where this resides in. Though your mileage may vary.