VARIANCE

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SELECT
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  category,
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  AVG(price) as avg_price,
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  VARIANCE(price) as price_variance,
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  STDDEV(price) as price_stddev,
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  SQRT(VARIANCE(price)) as stddev_from_variance
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FROM `project.dataset.products`
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GROUP BY category;

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SELECT
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  stock_symbol,
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  AVG(daily_return) as avg_return,
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  VARIANCE(daily_return) as return_variance,
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  SQRT(VARIANCE(daily_return)) as volatility
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FROM `project.dataset.stock_returns`
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WHERE trade_date >= DATE_SUB(CURRENT_DATE(), INTERVAL 1 YEAR)
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GROUP BY stock_symbol
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ORDER BY return_variance DESC
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LIMIT 10;

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SELECT
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  'Between Groups' as source,
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  VARIANCE(group_mean) * COUNT(DISTINCT department) as sum_of_squares
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FROM (
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  SELECT department, AVG(salary) as group_mean
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  FROM `project.dataset.employees`
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  GROUP BY department
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)
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UNION ALL
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SELECT
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  'Within Groups' as source,
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  SUM(group_variance * (group_count - 1)) as sum_of_squares
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FROM (
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  SELECT department, VARIANCE(salary) as group_variance, COUNT(*) as group_count
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  FROM `project.dataset.employees`
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  GROUP BY department
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);