Этот пример полезен для вас? Я нашел это на сайте nlog. Вы пробовали это?
<target xsi:type="Database" name="db">
<!-- SQL command to be executed for each entry -->
<commandText>INSERT INTO [LogEntries](TimeStamp, Message, Level, Logger) VALUES(getutcdate(), @msg, @level, @logger)</commandText>
<!-- parameters for the command -->
<parameter name="@msg" layout="${message}" />
<parameter name="@level" layout="${level}" />
<parameter name="@logger" layout="${logger}" />
<!-- connection string -->
<dbProvider>System.Data.SqlClient</dbProvider>
<connectionString>server=.\SQLEXPRESS;database=MyLogs;integrated security=sspi</connectionString>
<!-- commands to install database -->
<install-command>
<text>CREATE DATABASE MyLogs</text>
<connectionString>server=.\SQLEXPRESS;database=master;integrated security=sspi</connectionString>
<ignoreFailures>true</ignoreFailures>
</install-command>
<install-command>
<text>
CREATE TABLE LogEntries(
id int primary key not null identity(1,1),
TimeStamp datetime2,
Message nvarchar(max),
level nvarchar(10),
logger nvarchar(128))
</text>
</install-command>
<!-- commands to uninstall database -->
<uninstall-command>
<text>DROP DATABASE MyLogs</text>
<connectionString>server=.\SQLEXPRESS;database=master;integrated security=sspi</connectionString>
<ignoreFailures>true</ignoreFailures>
</uninstall-command>
</target>