如图，sql语句在数据库里可以正常运行但是再XML文件不可以正常运行，报错。

原因：在XML中小于号"<"是会被默认认定成文一个标签的开始，所以用小于号就会报错。

解决办法：

1.把表达式反过来改成大于号

2.用<![CDATA[ ]]>包起来，就不会被认定成为标签

   <![CDATA[
          AND (stt.class_date + stt.class_start_time::interval < CURRENT_TIMESTAMP
         OR (stt.class_date < CURRENT_DATE AND stt.class_start_time = '00:00:00'::time))
        ]]>

在这里我就展示一下用<![CDATA[ ]]>包起来的写法

        SELECT
            stt.id,stt.class_date,stt.class_start_time,stt.class_end_time,
            (SELECT COUNT(*) FROM study_time_table_study_student sttss2 WHERE sttss2.study_time_table_id = stt.id AND sttss2.used_status = 1) AS actual_num,
--         stt.actual_num,
            htm.teacher_name,htm.id as teacher_name_id,
            tcm.class_name,tcm.class_type,tcoum.course_name,tcoum.id as course_name_id,stt.study_course_id,
            sttss.study_student_id as student_id,ss.sts_student_name,ss.sts_phone
        FROM study_time_table stt
                 JOIN
             teach_class_manage tcm ON tcm.id = stt.study_class_id
                 JOIN
             teach_course_manage tcoum ON tcoum.id = stt.study_course_id
                 JOIN
             hr_teacher_manage htm ON htm.id = stt.hr_teacher_id
                 LEFT JOIN
             study_time_table_study_student sttss ON stt.id = sttss.study_time_table_id
                 JOIN
             study_student ss ON ss.id  = sttss.study_student_id
        where 1=1 AND stt.deleted = 0
          AND sttss.used_status = 0
        <![CDATA[
          AND (stt.class_date + stt.class_start_time::interval < CURRENT_TIMESTAMP
         OR (stt.class_date < CURRENT_DATE AND stt.class_start_time = '00:00:00'::time))
        ]]>