That's happened because somewhere called TFDQuery.ExecSQL or TFDStoredProc.ExecProc but SQL stored proc return result set, which obviously not fetched but not discard. And now any attempt to StartTransaction (internally it's just turn off autocommit) will be failed with this "clear and detailed" error message.
There's two options - call Query.Disconnect(True) or call Open instead ExecSQL\ExecProc.
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Delphi 10.4, FireDac, StartTransaction causes ODBC error.
in Databases
Posted · Edited by Michael Longneck
That's happened because somewhere called TFDQuery.ExecSQL or TFDStoredProc.ExecProc but SQL stored proc return result set, which obviously not fetched but not discard. And now any attempt to StartTransaction (internally it's just turn off autocommit) will be failed with this "clear and detailed" error message.
There's two options - call Query.Disconnect(True) or call Open instead ExecSQL\ExecProc.