### VAR_SAMP Function
```
var_samp([distinct] expr)
```
#### Function Description
The VAR_SAMP function is used to calculate the sample variance of a set of numerical data. Variance is a statistical measure of the dispersion of data distribution, reflecting the degree of deviation of data from its mean value. By calculating the variance, we can understand the fluctuation of the data, thereby evaluating the stability and reliability of the data.

#### Parameter Description
- `expr`: Numerical types, including tinyint, smallint, int, bigint, float, double, and decimal. Represents the numerical data for which the variance needs to be calculated.
- `distinct` (optional): Indicates the calculation of the variance of the distinct set. If this parameter is not set, the variance of the set including duplicate values is calculated.

#### Return Result
- Returns a double type value, representing the calculated sample variance.
- If all input values are null, null is returned.

#### Usage Example
1. Calculate the sample variance including duplicate values:
   ```sql
   SELECT var_samp(col) FROM VALUES (1), (2), (3), (3), (null) AS tab(col);
   ```
Result:
   ```
   0.9166666666666666
   ```
2. Calculate the sample variance after deduplication:
   ```sql
   SELECT var_samp(DISTINCT col) FROM VALUES (1), (2), (3), (3), (null) AS tab(col);
   ```
Result:
   ```
   1.0
   ```
3. Calculate the sample variance of student scores (assuming the score column is score):
   ```sql
   SELECT var_samp(score) FROM students;
   ```
4. Calculate the variance of the deduplicated product prices (assuming the price column is price):
   ```sql
   SELECT var_samp(DISTINCT price) FROM products;
   ```
#### Notes
- When there is only one value in the dataset, the VAR_SAMP function will return 0 because there is not enough data to calculate the variance.
- If all input values are null, the function will return null.
- In practical applications, attention should be paid to the accuracy and completeness of the data to avoid affecting the variance calculation results.

Through the above content, you can better understand the usage and notes of the VAR_SAMP function. In actual work, you can flexibly use this function as needed to analyze and evaluate data.