What are aggregate functions in MYSQL?

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In MySQL, aggregate functions are functions that perform a calculation on a set of values and return a single value. These functions are often used in conjunction with the SELECT statement to perform operations on a specific column or a set of columns in a table. Aggregate functions are useful for tasks like calculating the total sum, average, minimum, maximum, or counting the number of rows that meet a certain condition within a dataset.

Here are some common aggregate functions in MySQL:

  1. SUM(): Calculates the sum of values in a numeric column.

    sql code
    SELECT SUM(column_name) FROM table_name;

  2. AVG(): Calculates the average of values in a numeric column.

    sql code
    SELECT AVG(column_name) FROM table_name;

  3. COUNT(): Counts the number of rows in a result set, or counts the number of non-null values in a specific column.

    sql code
    SELECTCOUNT(*) FROM table_name; SELECT COUNT(column_name) FROM table_name;

  4. MAX(): Returns the maximum value in a column.

    sql code
    SELECTMAX(column_name) FROM table_name;

  5. MIN(): Returns the minimum value in a column.

    sql code
    SELECTMIN(column_name) FROM table_name;

  6. GROUP_CONCAT(): Concatenates values from multiple rows into a single string, grouped by a specified column.

    sql code
    SELECT GROUP_CONCAT(column_name) FROM table_name GROUPBY group_column;

  7. GROUP BY: Groups rows that have the same values in specified columns into aggregated data, like SUM, COUNT, AVG, etc.

    sql code
    SELECT column_name, SUM(another_column) FROM table_name GROUPBY column_name;

When using aggregate functions with GROUP BY, you can perform calculations on subsets of data based on the values in one or more columns. This is particularly useful in generating reports and summaries from large datasets.

Explain with example.

Let's assume we have a table called sales with the following structure:

sql code
CREATETABLE sales ( id INTPRIMARY KEY, product_name VARCHAR(255), category VARCHAR(50), amount INT );

And it contains some sample data:

|id|product_name|category|amount||----|--------------|----------|--------||1|ProductA|Electronics|500||2|ProductB|Clothing|300||3|ProductC|Electronics|800||4|ProductD|Electronics|700||5|ProductE|Clothing|400|

Now, let's look at examples of using aggregate functions in MySQL:

1. SUM():

To calculate the total sales amount:

sql code
SELECTSUM(amount) as total_sales FROM sales; -- Output: 2700

2. AVG():

To calculate the average sales amount:

sql code
SELECTAVG(amount) as average_sales FROM sales; -- Output: 540

3. COUNT():

To count the number of sales entries:

sql code
SELECT COUNT(*) as total_sales_entries FROM sales; -- Output: 5

4. MAX():

To find the maximum sales amount:

sql code
SELEC TMAX(amount) as max_sales FROM sales; -- Output: 800

5. MIN():

To find the minimum sales amount:

sql code
SELECT MIN(amount) as min_sales FROM sales; -- Output: 300

6. GROUP BY with SUM():

To find the total sales amount for each category:

sql code
SELECT category, SUM(amount) as total_sales FROM sales GROUPBY category; -- Output:-- | category | total_sales |-- |------------|-------------|-- | Electronics | 2000 |-- | Clothing | 700 |

7. GROUP_CONCAT():

To concatenate product names within each category:

sql code
SELECT category, GROUP_CONCAT(product_name) as products FROM sales GROUPBY category; -- Output:-- | category | products |-- |------------|------------------------------|-- | Electronics | Product A,Product C,Product D |-- | Clothing | Product B,Product E |

These examples demonstrate how you can use aggregate functions and the GROUP BY clause to perform calculations and generate summaries based on specific columns or groups in your MySQL database.

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