SELECT Username FROM Users WHERE Email = @Email

<sql-query name="SelectUsersByEmail">
        <return alias="Users" class="SimpleUser" />
        exec SelectUsersByEmail :Email
    </sql-query>

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
      assembly="NHBlog.Domain" namespace="NHBlog.Domain">
  <class name="BlogPost" table="BlogPost">
    <id name="ID" column="ID" type="int">
      <generator class="native" />
    </id>
    <property name="Title" column="Title" type="string" not-null="true"></property>
    <property name="Body" column="Body" type="string" not-null="true"></property>
    <property name="PublishedOn" column="PublishedOn" type="DateTime"></property>
    <many-to-one name="PublishedBy" column="PublishedByID" class="BlogUser" not-null="true" />
    <bag name="Comments" cascade="delete" inverse="true" >
      <key column="BlogPostID" />
      <one-to-many class="Comment" />
      <loader query-ref="GetCommentsByBlogPostID"/>
    </bag>
  </class>
  <sql-query name="GetCommentsByBlogPostID">
    <load-collection alias="Comments" role="BlogPost.Comments" />
    exec GetCommentsByBlogPostID :blogPostID
  </sql-query>
</hibernate-mapping>