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> Use this file to discover all available pages before exploring further.

> 计算总体协方差值

# covarPopStable

<h2 id="covarPopStable">
  covarPopStable
</h2>

引入版本：v1.1.0

计算总体协方差：

$$
\frac{\Sigma{(x - \bar{x})(y - \bar{y})}}{n}
$$

<br />

该函数与 [`covarPop`](/reference/functions/aggregate-functions/covarPop) 函数类似，但采用数值稳定算法。因此，`covarPopStable` 的速度比 `covarPop` 慢，但计算结果更为精确。

**语法**

```sql theme={null}
covarPopStable(x, y)
```

**参数**

* `x` — 第一个变量。[`(U)Int*`](/reference/data-types/int-uint) 或 [`Float*`](/reference/data-types/float) 或 [`Decimal`](/reference/data-types/decimal)
* `y` — 第二个变量。[`(U)Int*`](/reference/data-types/int-uint) 或 [`Float*`](/reference/data-types/float) 或 [`Decimal`](/reference/data-types/decimal)

**返回值**

返回 `x` 与 `y` 之间的总体协方差。[`Float64`](/reference/data-types/float)

**示例**

**使用稳定算法计算基本总体协方差**

```sql title=Query theme={null}
DROP TABLE IF EXISTS series;
CREATE TABLE series(i UInt32, x_value Float64, y_value Float64) ENGINE = Memory;
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);

SELECT covarPopStable(x_value, y_value)
FROM series
```

```response title=Response theme={null}
┌─covarPopStable(x_value, y_value)─┐
│                         6.485648 │
└──────────────────────────────────┘
```