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64 lines
1.5 KiB
Markdown
64 lines
1.5 KiB
Markdown
---
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title: "varSampStable"
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slug: /en/sql-reference/aggregate-functions/reference/varsampstable
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sidebar_position: 213
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---
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## varSampStable
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Calculate the sample variance of a data set. Unlike [`varSamp`](../reference/varsamp.md), this function uses a numerically stable algorithm. It works slower but provides a lower computational error.
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**Syntax**
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```sql
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varSampStable(x)
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```
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Alias: `VAR_SAMP_STABLE`
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**Parameters**
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- `x`: The population for which you want to calculate the sample variance. [(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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- Returns the sample variance of the input data set. [Float64](../../data-types/float.md).
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**Implementation details**
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The `varSampStable` function calculates the sample variance using the same formula as the [`varSamp`](../reference/varsamp.md):
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$$
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\sum\frac{(x - \text{mean}(x))^2}{(n - 1)}
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$$
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Where:
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- `x` is each individual data point in the data set.
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- `mean(x)` is the arithmetic mean of the data set.
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- `n` is the number of data points in the data set.
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**Example**
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Query:
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```sql
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DROP TABLE IF EXISTS test_data;
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CREATE TABLE test_data
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(
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x Float64
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)
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ENGINE = Memory;
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INSERT INTO test_data VALUES (10.5), (12.3), (9.8), (11.2), (10.7);
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SELECT round(varSampStable(x),3) AS var_samp_stable FROM test_data;
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```
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Response:
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```response
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┌─var_samp_stable─┐
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│ 0.865 │
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└─────────────────┘
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```
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