Question

我想像这样在表中插入行：我的专栏是学生，科目，班级，老师，级别。主键是（学生，主题）。该表包含所有学生，但是其中一些学生缺少数学科目，因此我想添加它而不复制那些已经有的学生。

我已经尝试过了，但是它给了我违反的独特约束：

insert into table (student,subject,class,teacher,level)
select a.student, 'math', null, null, null
from   table  a
where  a.student in (select distinct student from table where subject not in 'math') 
and    (a.student,a.subject) not in (select student,subject from table);

Answer 1

我认为您基本上需要select distinct：

insert into table (student, subject) 
    select distinct a.student, 'math'
    from table a
    where not exists (select 1
                      from table a2
                      where a2.student = a.student and
                            a2.subject = 'math'
                     );

Answer 2

一种方法是使用minus：

insert into course_students (student, subject) 
select student, 'Math' from course_students
minus
select student, subject from course_students;

如果您想在insert中包括其他列，则需要扩展一点：

insert into course_students (student, subject, class, teacher, course_level)
select student, subject, '101', 'Naomi', 1
from   ( select student, 'Math' as subject from course_students
         minus
         select student, subject from course_students );

如何在不复制现有数据的情况下插入新行

2 个答案: