Question

我有一个包含项目和作业的数据库。每个作业都链接到一个项目，但项目可以有多个作业。如何选择所有未归档但其关联分配都具有特定状态（付费）的项目？以下结果产生了预期的结果，因为我目前没有具有多个任务的项目，但是如果我这样做会有效吗？

SELECT projects.*
FROM projects,
     assignments
WHERE projects.id=assignments.project_id
  AND assignments.status='Paid'
  AND projects.archived='N'

Answer 1

试试这个：

SELECT p.*
FROM projects p
WHERE NOT EXISTS
(SELECT 1
 FROM assignments a
 WHERE p.id = a.project_id AND a.status <> 'Paid'
)
AND p.archived='N';

SQL Fiddle demo

Answer 2

尝试LEFT JOIN可能你想要这个

SELECT projects.*
FROM projects LEFT JOIN assignments
ON projects.id=assignments.project_id
WHERE assignments.status='Paid'
  AND projects.archived='N'

Answer 3

SELECT *
FROM projects WHERE projects.archived='N' AND projects.id IN(
SELECT s.id FROM projects p,assignments s WHERE p.id=s.id
AND s.status='Paid');

试试这个可行。

如果WHERE子句适用于多行，是否所有行都经过测试？

3 个答案: