What is the GROUP BY clause in SQL?
The GROUP BY clause in SQL is used to group rows in a table based on the values of one or more columns. This can be useful for summarizing data or identifying trends. For example, you could use the GROUP BY clause to group rows in a table of sales data by product category to see which categories are selling the best.
Here is a simple example of how to use the GROUP BY clause in SQL:
Create a table:
CREATE TABLE `sales` ( `product_category` VARCHAR(255) NOT NULL, `quantity` INT NOT NULL );
Insert data into the table:
INSERT INTO `sales` (`product_category`, `quantity`) VALUES
('Electronics', 10),
('Electronics', 20),
('Clothing', 30),
('Clothing', 40),
('Food & Beverage', 50),
('Food & Beverage', 60);
Use the GROUP BY clause to group the rows by product category and count the number of sales for each category:
SELECT product_category, COUNT(*) AS total_sales FROM sales GROUP BY product_category;
The GROUP BY clause has grouped the rows in the sales table by product category and then counted the number of rows in each group. The results show that the Food & Beverage category has the most sales, followed by the Clothing category and then the Electronics category
You can also use the GROUP BY clause to summarize the data in each group using aggregate functions, such as SUM(), AVG(), and MAX(). For example, the following query uses the SUM() function to calculate the total sales for each product category:
SELECT product_category, SUM(quantity) AS total_sales FROM sales GROUP BY product_category;
As you can see, the GROUP BY clause is a powerful tool for organizing and summarizing data in SQL. By understanding how to use the GROUP BY clause correctly, you can write more efficient and effective SQL queries.
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