To show the sql in the output window of Visual Studio, configure log4net to use TraceAppender in your log4net config. This:

<appender name="DebugSQL" type="log4net.Appender.TraceAppender">  
 <layout type="log4net.Layout.PatternLayout">  
        <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />  
 </layout>  

Then this:

<logger name="NHibernate.SQL" additivity="false">
<level value="DEBUG" />
<appender-ref ref="DebugSQL" />

EDIT: I can't seem to format this correctly here. See this link for code example

To show the SQL in the output window of Visual Studio, configure log4net to use TraceAppender in your log4net config. This:

<appender name="DebugSQL" type="log4net.Appender.TraceAppender"> 
    <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" /> 
    </layout>
</appender>

Then this:

<logger name="NHibernate.SQL" additivity="false">
    <level value="DEBUG" />
    <appender-ref ref="DebugSQL" />
</logger>

EDIT: I can't seem to format this correctly here. See this link for code example