Typical symptom: QMYSQL driver not loaded. Solution: get pre-built Qt SQL driver plug-in required to establish a connection to MySQL / MariaDB using Qt. Download qsqlmysql.dll binaries built from official Qt source code
Qt OCI Oracle database driver. Resolve "Driver not loaded" runtime error. Download pre-built qsqloci.dll driver library for establishing a database connection to Oracle Database using addDatabase("QOCI")