In Microsoft SQL Server, in-built functions provide a wide range of tools for manipulating and analyzing data. This chapter explores various categories of in-built functions and their real-world use cases.
Notes
1. GROUP BY Clause
The GROUP BY clause in Microsoft SQL Server is used to group rows with similar values in one or more columns into summary rows. It is essential for aggregating and summarizing data.
Basic GROUP BY Syntax:
Example :
Basic GROUP BY clause
SELECT
Department, AVG(Salary)
AS
AvgSalary
FROM
Employees
GROUP BY
Department;
In this example, the GROUP BY clause groups employees by their department, and the AVG function calculates the average salary for each department.
2. Aggregating Data (SUM, AVG, COUNT, etc.)
Aggregate functions in SQL Server allow you to perform calculations on groups of rows defined by the GROUP BY clause. Common aggregate functions include SUM, AVG, COUNT, MIN, and MAX.
Using Aggregate Functions:
Example :
Using SUM with GROUP BY
SELECT
Department, SUM(Salary)
AS
TotalSalary
FROM
Employees
GROUP BY
Department;
This query calculates the total salary for each department by using the SUM aggregate function.
3. Real-world GROUP BY Usage
E-commerce System:
- Sales by Category: Use GROUP BY to categorize products by type and calculate total sales for each category.
- Customer Analytics: Aggregate customer data to analyze buying patterns, such as average purchase amount or frequency of orders.
Finance System:
- Expense Reports: Group expenses by category or department to create expense reports and track spending.
- Income Analysis: Calculate average income and expenses for different income groups or regions.
4. Key Takeaways
- The GROUP BY clause is used to group rows based on one or more columns.
- Aggregate functions like SUM, AVG, COUNT, MIN, and MAX are used with GROUP BY to perform calculations on grouped data.
- Real-world scenarios often involve using GROUP BY and aggregate functions to summarize and analyze data.
5. Exercise Questions
- Write a query to calculate the total number of orders placed by each customer using GROUP BY and COUNT.
- Create a query that groups products by category and calculates the average price for each category using GROUP BY and AVG.
- Find the department with the highest total salary using GROUP BY and MAX.
- Generate a report that lists the most common medical conditions and their occurrence count in a healthcare database using GROUP BY and COUNT.
- Explain the importance of using aliases for columns generated by aggregate functions in the GROUP BY clause.
- Discuss the performance considerations when working with large datasets and complex aggregations using GROUP BY and aggregate functions.
In Microsoft SQL Server, User-Defined Functions (UDFs) are custom functions that allow you to encapsulate logic and perform specific tasks. This chapter explores the creation, usage, and real-world applications of UDFs.