回答編集履歴
3
distinct を書き忘れる痛恨のミス
test
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@@ -9,6 +9,8 @@
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.where(country: { area: 3 })
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.where(user: { id: 20 })
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+
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.distinct
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.count(:language)
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@@ -22,20 +24,20 @@
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```sql
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-
(0.
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(0.4ms)
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SELECT COUNT("questions"."language")
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SELECT COUNT(DISTINCT "questions"."language")
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FROM "questions"
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FROM "questions"
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INNER JOIN "units" ON "units"."id" = "questions"."unit_id"
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INNER JOIN "units" ON "units"."id" = "questions"."unit_id"
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INNER JOIN "subjects" ON "subjects"."id" = "units"."subject_id"
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INNER JOIN "subjects" ON "subjects"."id" = "units"."subject_id"
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INNER JOIN "users" user ON user."id" = "subjects"."user_id"
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INNER JOIN "users" user ON user."id" = "subjects"."user_id"
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INNER JOIN "countries" country ON country."id" = user."country_id"
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INNER JOIN "countries" country ON country."id" = user."country_id"
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WHERE "country"."area" = ? AND "user"."id" = ? [["area", 3], ["id", 2]]
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WHERE "country"."area" = ? AND "user"."id" = ? [["area", 3], ["id", 20]]
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```
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2
カウントを取得するSQLに修正
test
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@@ -1,61 +1,41 @@
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1
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> - countryのareaカラムが3
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-
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3
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1
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これでどうでしょうか？
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の条件に合う Question であれば、以下のコードで取得できます。
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2
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3
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```rb
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Question.joins(unit: { subject: { user: :country } })
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language_count = Question.joins(unit: { subject: { user: :country } })
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8
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.where(country: { area: 3 })
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9
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.where(country: { area: 3 })
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10
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.where(user: { id: 20 })
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.where(user: { id: 20 })
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.count(:language)
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```
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-
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生成されるSQLは以下の通りです。
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-
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```sql
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(0.2ms)
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SELECT COUNT("questions"."language")
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-
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FROM "questions"
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INNER JOIN "units" ON "units"."id" = "questions"."unit_id"
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INNER JOIN "subjects" ON "subjects"."id" = "units"."subject_id"
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INNER JOIN "users" user ON user."id" = "subjects"."user_id"
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-
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INNER JOIN "countries" country ON country."id" = user."country_id"
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```rb
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languages = Question.joins(unit: { subject: { user: :country } })
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.where(country: { area: 3 })
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-
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.where(user: { id: 20 })
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-
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.distinct(:language)
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-
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.pluck(:language)
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-
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-
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-
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WHERE "country"."area" = ? AND "user"."id" = ? [["area", 3], ["id", 2]]
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40
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```
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-
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-
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-
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しかし、「language が重複していたら、そのうちの1レコードを取得」という結果を求められているのであれば、重複時にどういう条件に基づいてレコードを取得するのかを決める必要があります。
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1
誤字修正
test
CHANGED
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@@ -32,7 +32,9 @@
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もし、単純に重複なしの language のリストを取得したいなら、
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-
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`.distinct(:language).pluck(:language)` を加えればよいです。
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