我有三张桌子:
project (idproject, name)
color (idcolor, name)
project_has_color (idproject, idcolor)
现在我需要选择与一组颜色相关的项目,例如:blue(1),red(2),green(3):
SELECT p.idproject, p.name
FROM project p, project_has_color c
WHERE p.idproject=c.idproject AND c.idcolor IN (1,2,3)
给了我与一个或多个给定idcolor连接的项目,我需要与所有相关的项目 - 但我无法弄清楚如何实现这一目标?
答案 0 :(得分:5)
使用JOIN是最可靠的方式:
SELECT p.idproject,
p.name
FROM PROJECT p
JOIN PROJECT_HAS_COLOR phc ON phc.idproject = p.idproject
JOIN COLOR c1 ON c1.idcolor = phc.idcolor
AND c1.idcolor = 1
JOIN COLOR c2 ON c2.idcolor = phc.idcolor
AND c2.idcolor = 2
JOIN COLOR c3 ON c3.idcolor = phc.idcolor
AND c3.idcolor = 3
使用:
SELECT p.idproject,
p.name
FROM PROJECT p
JOIN PROJECT_HAS_COLOR phc ON phc.idproject = p.idproject
JOIN COLOR c ON c.idcolor = phc.idcolor
WHERE c.idcolor IN (1, 2, 3)
GROUP BY p.idproject, p.name
HAVING COUNT(*) = 3
...依靠您的数据模型阻止idcolor
值多次与项目关联。您不能在MySQL中使用HAVING COUNT(DISTINCT *)
,因此同一项目的2个以上关系将复制idcolor
值将返回误报。
答案 1 :(得分:0)
这可能有用
SELECT p.idproject, p.name
FROM project p JOIN project_has_color c USING (idproject)
WHERE c.idcolor IN (1,2,3)
HAVING count(*)=3;
前提是项目不能与颜色相关联两次(即(idproject,idcolor)是唯一的)。或
HAVING
count(CASE WHEN c.idcolor=1 THEN 1 ELSE NULL)>0
AND count(CASE WHEN c.idcolor=2 THEN 1 ELSE NULL)>0
AND count(CASE WHEN c.idcolor=3 THEN 1 ELSE NULL)>0;
否则。