SQL4Automation is one of the best solution to connect PLC with a database.
It connects PLC directly with SQL databases.
SQL4Automation uses ODBC server for connecting PLC with database. OPC server is not required .Security and performances increases due to this. No project specific configuration is required. Everything is programmed in the controller.
SQL4Automation can be downloaded from the following link
Compatibility - 1.Rockwell Automation 2.CODESYS 3.Siemens S7 4.Rexroth 5.ABB 6.FESTO 7.WAGO