Question

我有两张桌子。一个是Course表，第二个是Teacher表。我希望得到所有Teacher不教'Math'的人。我怎么能这样做？

课程表

course_id   course  teacher_id  marks
 1          Physics     1        60
 2          Math        1        60
 3          Chemestry   1        60
 4          English     2        60
 5          Hindi       2        60
 6          Physics     2        60
 7          Chemestry   3        60
 8          English     4        60
 9          Math        5        60
10          Math        6        60

教师表

teacher_id  name      salary    gender
   1       Teacher1    20         1
   2       Teacher2    30         1
   3       Teacher3    40         2
   4       Teacher4    50         2
   5       Teacher5    60         1
   6       Teacher6    70         2

Answer 1

我希望得到所有不教数学的老师。

您需要加入 teacher_id 上的两个表格，然后根据课程过滤掉这些行。

SQL> SELECT DISTINCT t.name
  2  FROM course c,
  3    teacher t
  4  WHERE c.teacher_id = t.teacher_id
  5  AND c.course     <> 'Math';

NAME
--------
Teacher2
Teacher1
Teacher4
Teacher3

SQL>

编辑由于您有老师教授多门课程，您需要进一步过滤：

SQL> WITH DATA AS
  2    (SELECT c.*,
  3      t.name
  4    FROM course c,
  5      teacher t
  6    WHERE c.teacher_id = t.teacher_id
  7    AND c.course      <> 'Math'
  8    )
  9  SELECT DISTINCT name
 10  FROM data
 11  WHERE teacher_id NOT IN
 12    (SELECT teacher_id FROM course WHERE course = 'Math'
 13    )
 14  /

NAME
--------
Teacher2
Teacher4
Teacher3

SQL>

注意请注意，使用 NOT EXISTS 子句的其他解决方案在性能方面更好，因为表扫描较少甚至是索引扫描。使用适当的索引，不存在的查询将是一种最佳方法。

Answer 2

select * 
from teacher t 
where not exists 
(select 1 from course c where c.teacher_id = t.teacher_id and c.course = 'Math')

@LalitKumarB 本是绝对正确的

Answer 3

内部联接

select t.teacher_id, t.name
from teacher t, Course c 
where c.course='math' and t.teacher_id=c.teacher_id;

修改

你可以使用join和subquery来做。

select * from course join teacher on course.teacher_id=teacher.teacher_id where teacher.teacher_id not in (select distinct teacher_id from course where course = 'Math')

Answer 4

Select * from Teacher 
join Course 
on Teacher.teacher.id = Course.teacher.id 
where Course.course != 'Math'

Answer 5

select 
    t.name
from teacher t 
left join course c 
on c.teacher_id = t.teacher_id 
    where  c.course_id <> 2

给出所有不教数学的老师的名字

5 个答案: