Question

所以我有这段代码：

    select gbg.manual_grade,
                gbm.title,
                u.user_id
from gradebook_grade as gbg

join course_users as cu on gbg.course_users_pk1 = cu.pk1
join users as u on cu.users_pk1 = u.pk1
join gradebook_main as gbm on gbg.gradebook_main_pk1 = gbm.pk1
join course_main as cm on gbm.crsmain_pk1 = cm.pk1

where (cm.course_id) = 'HUMA-1301-057IN-S12013' and (u.user_id) = 'bpugh'

而且，正如现在的代码一样，结果完全是我想要的。记录是唯一的，它们与正确的用户ID和分配对齐。但是还有一个我需要的专栏。

每当我添加这一行：

join gradebook_log as gbl on gbm.pk1 = gbl.gradebook_main_pk1

并将我的select语句修改为

   select gbg.manual_grade,
                gbm.title,
                u.user_id,
                gbl.grade

它从gradebook_log表中提取所有gbl.grade行，即使我只是尝试过滤掉用户名，但仍然有u.user_id的列，但是用户名没有我正在拉动所有这些额外的行正确匹配..知道为什么会这样吗？

Answer 1

在新表上缺少连接条件，看起来应该是：

select gbg.manual_grade,
                gbm.title,
                u.user_id,
                gbl.grade
from gradebook_grade as gbg    
join course_users as cu on gbg.course_users_pk1 = cu.pk1
join users as u on cu.users_pk1 = u.pk1
join gradebook_main as gbm on gbg.gradebook_main_pk1 = gbm.pk1
join course_main as cm on gbm.crsmain_pk1 = cm.pk1
join gradebook_log as gbl 
      on gbm.pk1 = gbl.gradebook_main_pk1
         AND u.pk1 = gbl.users_pk1  
where (cm.course_id) = 'HUMA-1301-057IN-S12013' and (u.user_id) = 'bpugh'

Answer 2

join gradebook_log as gbl 
      on gbm.pk1 = gbl.gradebook_main_pk1
and gbl.User_ForeignKey1 = u1.pkl
and gbl.CourseMain_ForeignKey2 = cm.pk1

认为您可能想要将外键添加到用户中（如果有的话，可以使用课程）并且可以尝试一下

表连接返回整个表中的每一行

2 个答案: