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55 lines
1.5 KiB
Markdown
55 lines
1.5 KiB
Markdown
---
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slug: /en/sql-reference/aggregate-functions/reference/covarpop
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sidebar_position: 121
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---
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# covarPop
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Calculates the population covariance:
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$$
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\frac{\Sigma{(x - \bar{x})(y - \bar{y})}}{n}
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$$
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:::note
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This function uses a numerically unstable algorithm. If you need [numerical stability](https://en.wikipedia.org/wiki/Numerical_stability) in calculations, use the [`covarPopStable`](../reference/covarpopstable.md) function. It works slower but provides a lower computational error.
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:::
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**Syntax**
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```sql
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covarPop(x, y)
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```
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**Arguments**
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- `x` — first variable. [(U)Int*](../../data-types/int-uint.md), [Float*](../../data-types/float.md), [Decimal](../../data-types/decimal.md).
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- `y` — second variable. [(U)Int*](../../data-types/int-uint.md), [Float*](../../data-types/float.md), [Decimal](../../data-types/decimal.md).
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**Returned Value**
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- The population covariance between `x` and `y`. [Float64](../../data-types/float.md).
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**Example**
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Query:
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```sql
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DROP TABLE IF EXISTS series;
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CREATE TABLE series(i UInt32, x_value Float64, y_value Float64) ENGINE = Memory;
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INSERT INTO series(i, x_value, y_value) VALUES (1, 5.6, -4.4),(2, -9.6, 3),(3, -1.3, -4),(4, 5.3, 9.7),(5, 4.4, 0.037),(6, -8.6, -7.8),(7, 5.1, 9.3),(8, 7.9, -3.6),(9, -8.2, 0.62),(10, -3, 7.3);
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```
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```sql
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SELECT covarPop(x_value, y_value)
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FROM series;
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```
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Result:
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```reference
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┌─covarPop(x_value, y_value)─┐
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│ 6.485648 │
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└────────────────────────────┘
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```
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