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MySQL Aggregate Functions.md
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‎MySQL Aggregate Functions.md

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原文地址：https://www.mysqltutorial.org/mysql-aggregate-functions/
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# MySQL Aggregate Functions
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**Summary**: in this tutorial, you will learn about MySQL aggregate functions including `AVG`, `COUNT`, `SUM`, `MAX` and `MIN.`
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## Introduction to MySQL aggregate functions
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An aggregate function performs a calculation on multiple values and returns a single value.
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For example, you can use the `AVG()` aggregate function that takes multiple numbers and returns the average value of the numbers.
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The following illustrates the syntax of an aggregate function:
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![image](https://github.com/user-attachments/assets/c66d31f3-ea73-44fc-84dc-7c472eeb7bee)
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In this syntax:
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- First, specify the name of the aggregate function e.g., `AVG()`. See the list of aggregate functions in the following section.
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- Second, use `DISTINCT` if you want to calculate based on distinct values or `ALL` in case you want to calculate all values including duplicates. The default is `ALL`.
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- Third, specify an expression that can be a column or an expression that involves column and arithmetic operators.
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The aggregate functions are often used with the `GROUP BY` clause to calculate an aggregate value for each group e.g., the average value by the group or the sum of values in each group.
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The following picture illustrates the `SUM()` aggregate function is used in conjunction with a `GROUP BY` clause:
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![image](https://github.com/user-attachments/assets/5e967602-cb0d-451d-b113-ab6f6f48619e)
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MySQL supports the following aggregate functions:
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| Aggregate function | Description |
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| :----------------------------------------------------------- | :----------------------------------------------------------- |
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| [AVG()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-avg/) | Return the summation of all non-NULL values in a set. |
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| [BIT_AND()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-bit_and/) | Perform a bitwise AND of values in a column of a table. |
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| [BIT_OR()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-bit_or/) | Perform a bitwise OR of values in a column of a table. |
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| [BIT_XOR()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-bit_xor/) | Perform a bitwise XOR of values in a column of a table. |
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| [COUNT()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-count/) | Return the number of rows in a group, including rows with NULL values. |
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| [COUNT(DISTINCT)](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-count-distinct/) | Count the number of unique values of a column in a table. |
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| [COUNT(IF)](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-count-if/) | Count the number of values that meet a specified condition. |
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| [GROUP_CONCAT()](https://www.mysqltutorial.org/mysql-group_concat/) | Return a concatenated string. |
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| [JSON_ARRAYAGG()](https://www.mysqltutorial.org/mysql-json/mysql-json_arrayagg/) | Return result set as a single JSON array. |
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| [JSON_OBJECTAGG()](https://www.mysqltutorial.org/mysql-json/mysql-json_objectagg/) | Return result set as a single JSON object. |
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| [MAX()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-max-function/) | Return the highest value (maximum) in a set of non-NULL values. |
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| [MIN()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-min/) | Return the lowest value (minimum) in a set of non-NULL values. |
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| [STDEV()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-standard-deviation/) | Return the summation of all non-NULL values in a set. |
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| [STDDEV_POP()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-standard-deviation/) | Return the population standard deviation. |
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| [STDDEV_SAMP()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-standard-deviation/) | Return the sample standard deviation. |
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| [SUM()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-sum/) | Return the summation of all non-NULL values a set. |
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| [SUM(IF)](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-sum-if/) | Perform conditional summation using the SUM and IF functions. |
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| [VAR_POP()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-variance/) | Return the summation of all non-NULL values in a set. |
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| [VAR_SAMP()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-var_samp/) | Return the sample variance of values in a column of a table. |
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| [VARIANCE()](https://www.mysqltutorial.org/mysql-aggregate-functions/mysql-variance/) | Return the population standard variance of all non-NULL values in a set. |
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## MySQL aggregate function examples
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We will use the `products` and `orderdetails` tables from the [sample database](https://www.mysqltutorial.org/getting-started-with-mysql/mysql-sample-database/) for demonstration:
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![image](https://github.com/user-attachments/assets/f4e2c839-0315-42f1-9c41-db6fc05e582b)
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### The AVG() function examples
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The `AVG()` function calculates the average value of a set of values. It ignores NULL in the calculation.
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```
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AVG(expression)Code language: SQL (Structured Query Language) (sql)
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```
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For example, you can use the `AVG` function to calculate the average buy price of all products in the `products` table by using the following query:
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```
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SELECT
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AVG(buyPrice) average_buy_price
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FROM
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products;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - AVG example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-AVG-example.png)
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The following example uses the `AVG()` function to calculate the average buy price for each product line:
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```
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SELECT
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productLine,
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AVG(buyPrice)
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FROM
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products
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GROUP BY productLine
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ORDER BY productLine;
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Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - AVG with GROUP BY example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-AVG-with-GROUP-BY-example.png)
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### The COUNT() function examples
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The `COUNT()` function returns the number of the values in a set.
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For example, you can use the `COUNT()` function to get the number of products in the `products` table as shown in the following query:
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```
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SELECT
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COUNT(*) AS total
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FROM
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products;Code language: PHP (php)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#4)
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![MySQL Aggregate Function - COUNT example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-COUNT-example.png)
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The following statement uses the `COUNT()` function with the `GROUP BY` clause to get the number of products for each product line:
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```
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SELECT
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productLine,
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COUNT(*)
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FROM
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products
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GROUP BY productLine
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ORDER BY productLine;
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Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - COUNT with GROUP BY example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-COUNT-with-GROUP-BY-example.png)
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### The SUM() function examples
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The `SUM()` function returns the sum of values in a set. The `SUM()` function ignores `NULL`. If no matching row is found, the `SUM()` function returns NULL.
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To get the total order value of each product, you can use the `SUM()` function in conjunction with the `GROUP BY` clause as follows:
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```
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SELECT
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productCode,
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SUM(priceEach * quantityOrdered) total
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FROM
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orderDetails
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GROUP BY productCode
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ORDER BY total DESC;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#6)
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![MySQL Aggregate Function - SUM example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-SUM-example.png)
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To see the result in more detail, you can [join](https://www.mysqltutorial.org/mysql-basics/mysql-join/) the `orderdetails` table to the `products` table as shown in the following query:
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```
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SELECT
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productCode,
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productName,
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SUM(priceEach * quantityOrdered) total
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FROM
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orderDetails
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INNER JOIN
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products USING (productCode)
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GROUP BY productCode
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ORDER BY total;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - SUM with JOIN example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-SUM-with-JOIN-example.png)
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### The MAX() function examples
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The `MAX()` function returns the maximum value in a set.
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```
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MAX(expression)Code language: SQL (Structured Query Language) (sql)
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```
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For example, you can use the `MAX()` function to get the highest buy price from the `products` table as shown in the following query:
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```
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SELECT
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MAX(buyPrice) highest_price
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FROM
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products;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#8)
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![MySQL Aggregate Function - MAX example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-MAX-example.png)
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The following statement uses the `MAX()` function with the `GROUP BY` clause to get the highest price per product line:
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```
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SELECT
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productLine, MAX(buyPrice)
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FROM
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products
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GROUP BY productLine
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ORDER BY MAX(buyPrice) DESC;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - MAX with GROUP BY example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-MAX-with-GROUP-BY-example.png)
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### The MIN() function examples
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The `MIN()` function returns the minimum value in a set of values.
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```
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MIN(expression)Code language: SQL (Structured Query Language) (sql)
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```
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For example, the following query uses the `MIN()` function to find the lowest price from the `products` table:
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```
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SELECT
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MIN(buyPrice) lowest_price
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FROM
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products;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#11)
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![MySQL Aggregate Function - MIN example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-MIN-example.png)
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The following example uses the `MIN()` function with the `GROUP BY` clause to get the lowest price per product line:
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```
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SELECT
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productLine,
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MIN(buyPrice)
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FROM
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products
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GROUP BY productLine
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ORDER BY MIN(buyPrice);Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - MIN with GROUP BY example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-MIN-with-GROUP-BY-example.png)
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### The GROUP_CONCAT() function example
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The `GROUP_CONCAT()` concatenates a set of strings and returns the concatenated string. See the following `employees` and `customers` tables:
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![img](https://www.mysqltutorial.org/wp-content/uploads/2019/09/customers-employees.png)
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The following statement uses the `GROUP_CONCAT()` function to return the sales staff and list of customers that each sales staff is in charge of:
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```
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SELECT
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firstName,
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lastName,
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GROUP_CONCAT(
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DISTINCT customername
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ORDER BY customerName) customers
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FROM
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employees
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INNER JOIN customers
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ON customers.salesRepEmployeeNumber = employeeNumber
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GROUP BY employeeNumber
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ORDER BY firstName , lastname;Code language: SQL (Structured Query Language) (sql)
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```
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[Try It Out](https://www.mysqltutorial.org/tryit/query/mysql-aggregate-functions/#1)
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![MySQL Aggregate Function - GROUP_CONCAT example](https://www.mysqltutorial.org/wp-content/uploads/2019/09/MySQL-Aggregate-Function-GROUP_CONCAT-example.png)
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In this tutorial, you have learned how to use the most commonly used MySQL aggregate functions.

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