Shrinking SQL Server database I have a question about SQL Server databases. 

I have initialized a database (let's say Configuration_DB) of size 120GB following with certain application installation. This application installation has taken up 20GB out of that 120GB DB space and 100 GB is left free.

Now if I run shrink job on that, will it be reduced to 20Gb (plus something) or how much it can be reduced to, although the Configuration_DB.mdf file has already taken 120 GB on disk.

Thanks.
You can shrink you database file using SQL Server Management Studio.


  
  In Object Explorer, connect to an instance of the SQL Server Database Engine and then expand that instance.
  Expand Databases and then right-click the database that you want to shrink.
  Point to Tasks, point to Shrink, and then click Files. 
  


Source: https://docs.microsoft.com/en-us/sql/relational-databases/databases/shrink-a-file

Please be advised, that the databse needs at least some free space to work. So don't shrink it all the way down to 20 GiB