how can I use vsphere snapshot to take a snapshot of a SQL database without snapshot the entire VM?
Do you already configured your VM so that it uses one vmdk to store nothing but the sql database ?
You can toogle the dependent/independent/ types for the single vDISK you don't wanna snapshot. But read the documentation first because there are 3 type possible. See VMware Independent Persistent Vs. Independent Non-Persistent Disk Mode | MVSourceCode - mvsourcecode
Regards,
Joerg