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MySQL aggregate functions are used to perform calculations on groups of data and return a single value. Common functions include: SUM(): Sum COUNT(): Count of non-null values AVG(): Average MIN(): Minimum value MAX(): Maximum value STDEV(): Standard deviation VARIANCE(): Variance GROUP_CONCAT( ): Connection string CORR(): Correlation coefficient REGEXP_REPLACE(): Regular expression replacement

**Commonly used aggregate functions in MySQL**

Aggregation functions are used to calculate a set of data and return a single value. There are a variety of aggregate functions available in MySQL that serve different purposes.

**1. SUM(): **

Find the sum of a numeric column.

**2. COUNT(): **

Count the number of non-null values in the column.

**3. AVG(): **

Calculate the average of a numeric column.

**4. MIN(): **

Returns the minimum value in the numeric column.

**5. MAX(): **

Returns the maximum value in the numeric column.

**6. STDEV(): **

Calculate the standard deviation of a numeric column.

**7. VARIANCE(): **

Calculate the variance of a numeric column.

**8. GROUP_CONCAT(): **

Concatenate the values in the specified column into a string.

**9. CORR(): **

Calculate the correlation coefficient between two numeric columns.

**10. REGEXP_REPLACE(): **

Use regular expressions to replace substrings in a string.

**Usage: **

Aggregation functions are often used with the GROUP BY clause to group data and then apply the aggregate function to each group. For example:

```
SELECT department, SUM(salary)
FROM employee
GROUP BY department;
```

This will sum employee salaries by department and return the total salary for each department.

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