回答編集履歴
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追記
test
CHANGED
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@@ -1,3 +1,111 @@
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group by 処理の場合、理論上「count(*)が0以下に集計される」ことはないので
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命題自体が達成できません
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# 追記
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一応サンプル付けておきます
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count(*) が0以下にならないのを理解しないことには先に進まないかと
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```SQL
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create table tbl(col1 varchar(10),col2 varchar(10),col3 int);
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insert into tbl values
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('A','X',10),
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('A','X',15),
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('A','X',12),
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('A','Y',20),
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('B','Y',35),
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('C','X',10),
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('C','X',11),
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('C','Z',8);
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```
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単純に集計
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```SQL
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select col1,col2,count(*) as count
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from tbl group by col1,col2
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order by col1 asc,col2 asc;
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```
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|col1|col2|count|
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|:--|:--|--:|
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|A|X|3|
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|A|Y|1|
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|B|Y|1|
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|C|X|2|
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|C|Z|1|
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## JOINして集計
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```SQL
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select t3.col1,t3.col2,coalesce(count,'NG') as count
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from (select distinct t1.col1,t2.col2 from tbl as t1,tbl as t2) as t3
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left join (select col1,col2,count(*) as count from tbl group by col1,col2) as t4
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on t3.col1=t4.col1 and t3.col2=t4.col2
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order by col1 asc,col2 asc;
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```
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|col1|col2|count|
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|:--|:--|--:|
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|A|X|3|
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|A|Y|1|
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|A|Z|NG|
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|B|X|NG|
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|B|Y|1|
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105
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|B|Z|NG|
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|C|X|2|
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|C|Y|NG|
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|C|Z|1|
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