Question

假设我有三个关系

部分（partno，partname，color）partno是P.K
  供应商（supplierno，sname）supplierno是P.K
  part_supplier（supplierno，partno）supplierno，partno是P.K。

现在我想得到供应部分只有一种颜色的供应商的名称。

Answer 1

有条款是你的朋友。

select field1, etc, count(*) records
from yourTables
where whatever
group by field1, etc
having count(*) = 1

Answer 2

Select sup.sname,count(*) from part_supplier Map
inner join supplier sup
on map.supplierno=sup.supplierno
inner join part par
on Map.partno=par.partno
group by sup.sname 
having count(*)=1

Answer 3

查询：

SELECT S.sname 
FROM part P, supplier S, part_supplier PS
WHERE S.supplierno = ps.supplierno AND
      PS.partno = P.partno
GROUP BY P.partno
HAVING count(P.color) = 1

表格：

CREATE TABLE supplier (
  supplierno     INT          PRIMARY KEY,
  suppliername   VARCHAR(10)  NOT NULL
);

CREATE TABLE part (
  partno     INT          PRIMARY KEY,
  partname   VARCHAR(10)  NOT NULL,
  color   INT          NOT NULL
);

CREATE TABLE part_supplier (
  supplierno INT          NOT NULL REFERENCES supplier(supplierno),
  partno     INT          NOT NULL REFERENCES part(partno),
  PRIMARY KEY (supplierno, partno)
);

一些测试数据：

INSERT INTO part VALUES (1, 'a',1), (2, 'b',2), (3, 'c',3), 
                        (4, 'd',1), (5, 'e',2), (6, 'c',3), 
                        (7, 'd',1), (8, 'e',2), (9, 'e',3);

INSERT INTO supplier VALUES (1,'a'), (2,'b'), (3,'c');

INSERT INTO part_supplier VALUES (1,1), (2,1), (3,3), 
                                 (4,1), (5,1), (6,1), 
                                 (7,2), (8,2), (9,3);

Answer 4

SELECT s.supplierno
FROM supplier AS s
JOIN part_supplier AS ps
  ON s.supplierno = ps.supplierno
JOIN part AS p
  ON ps.partno = p.partno
GROUP BY s.supplierno
HAVING COUNT(DISTINCT p.color) = 1 -- only one color for all parts

需要sql，一个棘手的

4 个答案: