elena belykh
72 lines
1.8 KiB
SQL
72 lines
1.8 KiB
SQL
--Задача 1
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В варианте А: WHERE фильтрует товары и убирает те, которые не в наличии, потом эти товары(строки)участвуют в группировке, в варианте В - HAVING фильтрует уже сгруппированные данные(категории)
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--Задача 2356
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SELECT teacher_id,
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COUNT(DISTINCT subject_id) AS cnt
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FROM teacher
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GROUP BY teacher_id;
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--Задача 1581
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SELECT customer_id,
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COUNT(v.visit_id) AS count_no_trans
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FROM visits v
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LEFT JOIN transactions t
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ON v.visit_id = t.visit_id
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WHERE t.transaction_id IS NULL
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GROUP BY customer_id;
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--Задача 1141
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SELECT activity_date AS day,
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COUNT(DISTINCT user_id) AS active_users
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FROM Activity
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WHERE activity_date BETWEEN '2019-06-28' AND '2019-07-27'
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GROUP BY activity_date;
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--Задача 596
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SELECT class
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FROM Courses
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GROUP BY class
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HAVING COUNT(student) >= 5;
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--Задача 1075
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SELECT project_id,
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ROUND(AVG(experience_years), 2) AS average_years
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FROM Project p
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JOIN Employee e
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ON p.employee_id = e.employee_id
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GROUP BY project_id;
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--Задача 1729
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SELECT user_id,
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COUNT (follower_id) AS followers_count
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FROM followers
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GROUP BY user_id
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ORDER BY user_id;
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--Задача 1633
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SELECT
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r.contest_id,
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ROUND(
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COUNT(r.user_id) * 100.0 / (SELECT COUNT(*) FROM Users),
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2
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) AS percentage
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FROM Register r
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GROUP BY r.contest_id
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ORDER BY percentage DESC, r.contest_id ASC;
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--Задача 1251
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SELECT
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p.product_id,
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COALESCE(
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ROUND(
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SUM(u.units * p.price) * 1.0 / NULLIF(SUM(u.units), 0),
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2
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),
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0
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) AS average_price
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FROM Prices p
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LEFT JOIN UnitsSold u
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ON p.product_id = u.product_id
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AND u.purchase_date BETWEEN p.start_date AND p.end_date
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GROUP BY p.product_id; |