MySQL MyBatis 默认插入当前时间

<!--单表动态更新语句 -->
  <update id="update" parameterType="com.zzg.entity.ColumnValidate">
  		update ucas_bus_column_validate
  		<set>
			<if test="updateBy != null and updateBy != ''">
				  update_by = #{updateBy,jdbcType=VARCHAR},
			</if>
      		<if test="state != null and state != ''">
        		`state` = #{state,jdbcType=VARCHAR},
      		</if>
      		<if test="deleteFlag != null and deleteFlag != ''">
        		delete_flag = #{deleteFlag,jdbcType=VARCHAR},
      		</if>
      		<if test="validateName != null and validateName != ''">
      			 validate_name =  #{validateName,jdbcType=VARCHAR},
      		</if>
      		<if test="validateContent != null and validateContent != ''">
      			 validate_content = #{validateContent,jdbcType=VARCHAR},
      		</if>
      		version = version + 1,
      		update_dt = now()
      	</set>
       	where sid = #{sid,jdbcType=VARCHAR} and version = #{version, jdbcType=INTEGER}
  </update>

重点代码：update_dt = now()