Where can I find instructions on odbc ConnectionStrings?

[rainspider]

Windows + qt 4.6.0 for opensource+ nmake

when i using ADO connection string, field.
eg:

Provider=SQLOLEDB.1;User ID=sa;Password=123456;Initial Catalog=NorthWind;Data Source=127.0.0.1

But use this connectionstring (come form qt help document),successful .
eg:

DRIVER={SQL Server};SERVER=127.0.0.1;UID=sa;PWD=12345;DATABASE =NorthWind

code:

QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
    db.setDatabaseName("connectionstring");

QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
    db.setDatabaseName("connectionstring");

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Who can tell me the difference between them ,or Where can i find the instructions on the connectionstrings?