What are the aggregate functions in mysql?

MySQL aggregate functions are used to calculate a single result of a set of data, including COUNT() (number of non-null values), SUM() (sum), AVG() (average), MAX() ( maximum value) and MIN() (minimum value). Additionally, there are STD() (standard deviation), VAR() (variance), GROUP_CONCAT() (concatenation of values), BIT_OR() (bitwise OR), and BIT_AND() (bitwise AND). These functions are often used with the GROUP BY clause to group data and perform calculations on each group.

Aggregation functions in MySQL

Aggregation functions are used to perform calculations on a set of data and return a single result. A variety of aggregate functions are provided in MySQL for processing different types of data.

Commonly used aggregate functions

• COUNT(): Count the number of non-null values ​​in the specified column.
• SUM(): Calculates the sum of all values ​​in the specified column.
• AVG(): Calculates the average of all values ​​in the specified column.
• MAX(): Returns the maximum value in the specified column.
• MIN(): Returns the minimum value in the specified column.

Other aggregate functions

In addition to the above basic aggregate functions, MySQL also provides some other aggregate functions to meet more advanced needs:

• STD(): Calculate the standard deviation.
• VAR(): Calculate the variance.
• GROUP_CONCAT(): Concatenate a set of values ​​into a string.
• BIT_OR(): Computes the bitwise OR of a set of integers.
• BIT_AND(): Computes the bitwise AND of a set of integers.

Using aggregate functions

Aggregation functions are typically used with a GROUP BY clause, which groups data and performs aggregate calculations for each group. For example:

<code>SELECT department, AVG(salary)
FROM employee
GROUP BY department;</code>

This query groups employees into departments and calculates the average salary for each department.

Note:

• Aggregation functions cannot be used to calculate DISTINCT values.
• Aggregation functions cannot be used to perform calculations on text columns.
• NULL values ​​are ignored unless special options are used, such as SUM(COALESCE()).

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