Double click on *.sql file opens another instance of SSMS
When you have:
1. SSMS set up as a default editor for *.sql files (and)
2. SSMS already started with "Connect to Database Engine" dialog window open
and you are trying open a .sql file by double-click, it starts another instance of SSMS and opens .sql file there.
My suggestion is to change the behavior to open the file in the exisiting instance of SSMS.
I would also suggest a fix for this issue be implemented. It is more annoying than anything having multiple windows up due to running several existing queries
Scott Bakker commented
This has been a problem for many years, many versions of SSMS. It happens for me after installing another application which takes over the file association for .SQL files, and I try to put it back to SSMS. Uninstalling and reinstalling SSMS doesn't help. Perhaps a "File Association Repair" option on the Tools menu? Or a smarter launch program?
Used to reuse an existing instance, recently changed along the way...
for me it doesn`t open file at all, just starts new instance of ssms