SQL COUNT记录JOINS远

Question

使用MySQL，我有三个表：

项目：

ID name 
1 "birthday party" 
2 "soccer match" 
3 "wine tasting evening" 
4 "dig out garden" 
5 "mountainbiking" 
6 "making music" 

批次：

ID projectID templateID when 
1 1   1   7 days before 
2 1   1   1 day before 
3 4   2   21 days before 
4 4   1   7 days before 
5 5   1   7 days before 
6 3   5   7 days before 
7 3   3   14 days before 
8 5   1   14 days before 

模板：

ID name message 
1 inf1 "Hi, I'd like to invite ..." 
2 for1 "Dear Sir, Madam, ..." 
3 can1 "Can you please ..." 
4 inf2 "Would you like to ..." 
5 all1 "To all dear friends ..." 
6 inf3 "Does any of you guys ..." 

我想显示模板表和他们所使用的项目数量 所以，结果应（更新！）：

templateName projectCount 
inf1   3 
for1   1 
can1   1 
inf2   0 
all1   1 
inf3   0 

我已经试过各种的SQL查询使用各种JOIN，但我想这对我来说太复杂了。是否有可能使用单个SQL语句获得此结果？

Answer 1

SELECT t.name templateName, COUNT(DISTICT b.projectID) projectCount 
FROM templates t 
LEFT OUTER JOIN batches b ON t.ID = b.templateID 
GROUP BY t.ID, t.name 
ORDER BY t.ID 

Answer 2

你尝试过这样的事情： -

SELECT TemplateId, COUNT(ProjectId) AS ProjectCount FROM Batches GROUP BY TemplateId 

Answer 3

从您提供的O/P所需的样本上述，我想，你希望templateId的数字作为一个projectCount

select templateID, count(templateID) as projectCount from batches group by templateID 

EDIT（AFTER问题编辑）

select t.name as templateName, count(b.templateID) as projectCount from batches b, templates t where b.templateID=t.id group by t.id 

Answer 4

我不知道MySQL的语法，但这个应该这样做：

SELECT t.name as templateName, COUNT(DISTINCT b.projectID) as projectCount 
FROM batches b 
INNER JOIN templates t 
    ON b.templateId = t.ID 
GROUP BY t.name 

Answer 5

Select TemplateId, 
     Count(distinct projectId) as ProjectCount, 
FROM batches 
Group By TemplateId 

我希望这应该工作。

我们需要不同的样本数据，我可以看到相同的模板和项目具有多行......