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SQL SELECT TOP
Introduction:
The SQL SELECT TOP clause is used to specify the number of records to return. It is useful for limiting the results in large datasets.
Syntax:
The basic syntax of the SELECT TOP clause is:
SELECT TOP(number) column_name(s)
FROM table_name;
Example 1:
Retrieve the top 5 employees from the Employees table:
SELECT TOP(5) * FROM Employees;
Example 2:
Retrieve the top 10 products ordered by price:
SELECT TOP(10) * FROM Products ORDER BY Price DESC;
Example 3:
Retrieve 20% of the top students based on their scores:
SELECT TOP 20 PERCENT * FROM Students ORDER BY Score DESC;
Important Note:
The SELECT TOP clause is not supported by all SQL dialects. For example, MySQL uses LIMIT, while Oracle uses ROWNUM.
Console Output Example:
[Sample Output]
Advanced Usage of SELECT TOP
Combining with WHERE Clause:
You can combine the SELECT TOP clause with a WHERE clause to filter results further.
SELECT TOP(3) * FROM Orders WHERE Status = 'Pending';
Using with JOIN:
The SELECT TOP clause can be used in queries involving JOIN operations.
SELECT TOP(5) Customers.Name, Orders.OrderID
FROM Customers
JOIN Orders ON Customers.CustomerID = Orders.CustomerID;
With Aggregation Functions:
Use the SELECT TOP clause along with aggregation functions like COUNT, SUM, etc.
SELECT TOP(1) Department, COUNT(EmployeeID) AS NumberOfEmployees
FROM Employees
GROUP BY Department
ORDER BY NumberOfEmployees DESC;
Caution:
Always ensure that your query returns the desired results, especially when using ORDER BY with SELECT TOP.
Console Output Example:
[Sample Output]
