Question

我有3张桌子

质量

id    name
----------
 1    bold
 2    Frank
 3    Quite
 4    friendly

学生

id name
---------
 1  A
 2  B
 3  C

StudentQuality

id  fk_qual  fk_stud
 1   1        1
 2   2        1
 3   1        2
 4   2        2
 5   3        2
 6   1        3
 7   2        3
 8   3        3
 9   4        3

这些是我的表格。我如何让那些大胆，坦诚和相当的学生。如果我使用IN操作，我会得到所有3名学生，我只需要2名学生如果我使用大胆，坦白，我应该得到所有3名学生如果我使用大胆，坦诚，相当友好，我应该得到所有1名学生那么如何查询。

Answer 1

你可以这样做：

声明一个表变量，保存您正在搜索的值
选择数据并使用表变量作为INNER JOIN的条件并计算表变量的值并将它们与质量值进行比较

像：

DECLARE  @qualities table(qname  varchar(100));
INSERT INTO   @qualities   
       VALUES ('bold'),('Frank'),('Quite');

       SELECT S.name
         FROM Student S
   INNER JOIN StudentQuality SQ
           ON S.id = SQ.fk_stud
   INNER JOIN Quality Q
           ON SQ.fk_qual = Q.id
          AND Q.name in (SELECT qname FROM @qualities)          
      GROUP BY S.name
      HAVING count(*) = (SELECT COUNT(qname) FROM @qualities)

Answer 2

SELECT *
FROM Student
WHERE id IN
(
  SELECT fk_stud 
  FROM StudentQuality sq
  JOIN Quality q ON sq.fk_qual = q.id
  WHERE q.name IN ('bold')
)
INTERSECT
SELECT *
FROM Student
WHERE id IN
(
  SELECT fk_stud 
  FROM StudentQuality sq
  JOIN Quality q ON sq.fk_qual = q.id
  WHERE q.name IN ('frank')
)
INTERSECT
SELECT *
FROM Student
WHERE id IN
(
  SELECT fk_stud 
  FROM StudentQuality sq
  JOIN Quality q ON sq.fk_qual = q.id
  WHERE q.name IN ('quite')
)

或没有INTERSECT

SELECT *
FROM Student
WHERE id IN
(
  SELECT fk_stud 
  FROM StudentQuality sq
  JOIN Quality q ON sq.fk_qual = q.id
  WHERE q.name IN ('bold')
) and id IN
(
  SELECT fk_stud 
  FROM StudentQuality sq
  JOIN Quality q ON sq.fk_qual = q.id
  WHERE q.name IN ('frank')
) and id IN
(
  SELECT fk_stud 
  FROM StudentQuality sq
  JOIN Quality q ON sq.fk_qual = q.id
  WHERE q.name IN ('quite')
)

Answer 3

另一种变化

SELECT s.id,min(s.name) studentname FROM student s
INNER JOIN (studentquality sq INNER JOIN quality q ON q.id=sq.fk_qual)
ON sq.fk_stud=s.id WHERE q.name in ('bold','frank','quite') group by s.id
having length(group_concat(q.name))=length(concat('bold,','frank,','quite'));

SELECT s.id,min(s.name) studentname, (group_concat(q.name)) qname FROM student s
INNER JOIN (studentquality sq INNER JOIN quality q ON q.id=sq.fk_qual)
ON sq.fk_stud=s.id WHERE q.name in ('bold','frank','quite') group by s.id
having length(qname)=length(concat('bold,','frank,','quite'));

如何编写SQL查询

3 个答案: