SQL - GROUP BY 有计数，连接多个表

Question

我有 4 张桌子：

Entries:
id
year
day

AnalysisText:
id
text
entries_id

AnalysisType:
id
type

AnalysisTextTypes:
id
analysistext_id
analysistype_id

示例数据：

entries     
id  year    day
1   2010    1
2   2011    4
3   2012    6


AnalysisText        
id  text    entries_id
1   blah    2
2   more blah   1
3   blah blah   1

AnalysisType        
id  type    
1   A   
2   B   
3   C   

AnalysisTextTypes       
id  analysistext_id analysistype_id
1   1   1
2   1   2
3   2   3
4   3   1

我需要获取具有多个analysistype 的所有analysistext 值，以及与具有多个analysistype 的这些analysistext 关联的所有entries。

所以在上面的数据中，我们想要结果

my_date text    type
2011-4  blah    A
2011-4  blah    B

因为那是具有不止一种类型的文本。

下面的查询有效，但是使用子查询来识别大于analysisType 的analysisText 值感觉效率低下：

select  
CONCAT(e.year, '-', e.day) as my_date,
x.text,
y.type
from entries e
join analysistext x on e.id = x.entries_id
join analysistext_types xy on xy.analysistext_id = x.id
join analysistype y on y.id = xy.analysistype_id
where xy.analysistext_id in (
    select analysistext_id
    from analysistext_types
    group by analysistext_id
    having count(analysistype_id) > 1
) order by my_date, analysis_text, type;

我想要一个查询，我们 SELECT 来自已连接表的感兴趣的字段，并直接在要连接的表上执行 group by 和 having count。这可能吗？

Answer 1

您可以使用自连接来完全避免子查询

select concat(e.year, '-' ,e.day), at.text ,ant.type
from AnalysisText at
join entries e on at.entries_id = e.id
join AnalysisTextTypes att on att.analysistext_id = at.id
join AnalysisType ant on att.analysistype_id = ant.id
join AnalysisTextTypes att2 on att2.analysistext_id = att.analysistext_id
group by att2.analysistext_id
having count(att2.analysistext_id) > 1