if

The most common thing to do in dynamic SQL is conditionally include a part of a where clause. For example:

<select id="findActiveBlogWithTitleLike"
     resultType="Blog">
  SELECT * FROM BLOG
  WHERE state = ‘ACTIVE’
  <if test="title != null">
    AND title like #{title}
  </if>
</select>

This statement would provide an optional text search type of functionality. If you passed in no title, then all active Blogs would be returned. But if you do pass in a title, it will look for a title like that (for the keen eyed, yes in this case your parameter value would need to include any masking or wildcard characters).

What if we wanted to optionally search by title and author? First, I’d change the name of the statement to make more sense. Then simply add another condition.

<select id="findActiveBlogLike"
     resultType="Blog">
  SELECT * FROM BLOG WHERE state = ‘ACTIVE’
  <if test="title != null">
    AND title like #{title}
  </if>
  <if test="author != null and author.name != null">
    AND author_name like #{author.name}
  </if>
</select>