回答編集履歴
2
追記
test
CHANGED
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@@ -15,3 +15,21 @@
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15
15
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```
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16
16
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17
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上記は相関副問合せでclassの人数を求めています。
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18
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+
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19
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+
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20
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+
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21
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+
レベルを揃えるならクロス集計
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22
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+
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23
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+
```SQL
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24
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+
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25
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+
SELECT class
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+
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+
, sum(gender='男') as man_count, , sum(gender='女') as woman_count
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28
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+
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29
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, sum(gender='男') / count(*) as man_per, sum(gender='女') / count(*) as woman_per
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+
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FROM student
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+
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GROUP BY class
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34
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+
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```
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1
推敲
test
CHANGED
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@@ -4,7 +4,9 @@
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4
4
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5
5
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```SQL
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6
6
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7
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+
SELECT class, gender, count(*) as count
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8
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+
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7
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-
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9
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, count(*) / (select count(*) from student where class=t1.class) as per
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8
10
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9
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FROM student
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10
12
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