Added Functions

Author: nidea1

Functions/Built-In Functions/Examples.sql

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+-- Examples
+
+-- COUNT
+SELECT COUNT(*) FROM Products;
+
+-- SUM
+SELECT SUM(UnitPrice) FROM Products;
+
+-- AVG
+SELECT AVG(UnitPrice) FROM Products;
+
+-- MAX MIN
+SELECT MAX(UnitPrice), MIN(UnitPrice) FROM Products;
+
+-- UCASE LCOSE
+SELECT UCASE(ProductName), LCASE(ProductName) FROM Products; --> Output -> TEST, test
+
+-- SUBSTRING
+SELECT SUBSTRING(ProductName, 1, 5) FROM Products; --> Output -> Alice Mutton to Alice
+
+-- ROUND
+SELECT ROUND(UnitPrice, 2) FROM Products; --> Output -> 21.35 to 21.40
+
+-- GETDATE
+SELECT OrderID, GETDATE() as CurrentDateTime FROM Orders;
+
+-- DATEDIFF
+SELECT OrderID, DATEDIFF(day, OrderDate, GETDATE()) as DaysFromOrderToNow FROM Orders;
+
+
+-- RANK ROWNUMBER
+
+SELECT 
+    OrderID, 
+    CustomerID, 
+    OrderDate,
+    RANK() OVER(ORDER BY OrderDate) as Rank,
+    ROW_NUMBER() OVER(ORDER BY OrderDate) as RowNumber
+FROM Orders;
+
+-- OUTPUT
+-- OrderID  CustomerID  OrderDATE               Rank    RowNumber
+-- 10248	VINET	    1996-07-04 00:00:00.000	1	    1
+
+
+-- LAG
+
+SELECT 
+    OrderID, 
+    CustomerID, 
+    OrderDate,
+    LAG(OrderDate) OVER(ORDER BY OrderDate) as PreviousOrderDate
+FROM Orders;
+
+-- OUTPUT
+-- OrderID  CustomerID  OrderDATE                   PreviousOrderDate
+-- 10248	VINET	    1996-07-04 00:00:00.000	    NULL
+-- 10249	TOMSP	    1996-07-05 00:00:00.000	    1996-07-04 00:00:00.000

Functions/README.md

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+# Functions
+
+One of the most powerful features of SQL is the ability to use functions to perform various operations on the data in a database.
+
+## Different Types of SQL Functions
+- **User Defined Functions:** These are functions that users create according to their own needs.
+- **Built-In Functions:** They are functions that are defined within SQL itself and are widely used.
+
+![img1](https://www.complexsql.com/wp-content/uploads/2017/03/SQL-Functions-1.jpg)

Functions/User Defined Functions/Examples.sql

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+-- Scalar Function -> returns one value
+
+-- Example
+
+CREATE FUNCTION AverageProductPrice()
+RETURNS money
+as
+BEGIN
+    RETURN (SELECT AVG(UnitPrice) FROM Products)
+END
+
+-- Test
+
+SELECT dbo.AverageProductPrice() AS AveragePrice
+
+
+-- Table-Valued Function -> returns table
+
+-- Example
+
+CREATE FUNCTION OrdersByCity(@city nvarchar(15))
+RETURNS TABLE
+as
+RETURN
+(
+    SELECT Orders.OrderID, Customers.CompanyName, Customers.ContactName
+    FROM Orders
+    JOIN Customers ON Orders.CustomerID = Customers.CustomerID
+    WHERE Customers.City = @city
+)
+
+-- Test
+
+SELECT * FROM dbo.OrdersByCity('London')
+
+
+-- Multi-Statement Table-Valued -> returns multi statement table
+
+-- Example
+
+CREATE FUNCTION OrderDetailsByProduct(@ProductID int)
+RETURNS @orderDetails TABLE 
+(
+   OrderID int,
+   ProductID int,
+   UnitPrice money,
+   Quantity smallint,
+   Discount real
+)
+as
+BEGIN
+   INSERT INTO @orderDetails
+   SELECT OrderID, ProductID, UnitPrice, Quantity, Discount
+   FROM [Order Details]
+   WHERE ProductID = @ProductID
+
+   RETURN
+END
+
+-- Test
+
+SELECT * FROM dbo.OrderDetailsByProduct(1)

Functions/User Defined Functions/Practices.sql

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+-- Orders by Employee
+
+CREATE FUNCTION OrderDetailsByEmployee(@EmployeeID INT)
+RETURNS TABLE
+as
+RETURN
+(
+    SELECT P.ProductID, P.ProductName, SUM(OD.UnitPrice * OD.Quantity * (1 - OD.Discount)) AS TotalPrice, SUM(OD.Quantity) as TotalQuantity, AVG(OD.Discount) as AvgDiscount, O.OrderDate
+    FROM Employees as E
+    JOIN Orders as O ON O.EmployeeID = E.EmployeeID
+    JOIN [Order Details] as OD ON O.OrderID = OD.OrderID
+    JOIN Products as P ON OD.ProductID = P.ProductID
+    WHERE E.EmployeeID = @EmployeeID
+    GROUP BY P.ProductID, P.ProductName, O.OrderDate
+)
+
+-- Test
+SELECT * FROM OrderDetailsByEmployee(5)
+
+
+-- Product Name and Product Price by Employee
+-- If ID <= 0 returns ID = 0, ProductName = Invalid Employee ID, TotalPrice = 0
+
+CREATE FUNCTION ProductDetailsByEmployee(@EmployeeID INT)
+RETURNS @ProductsByEmployee TABLE
+(
+    ID INT,
+    ProductName NVARCHAR(50),
+    TotalPrice MONEY
+)
+as
+BEGIN
+    IF @EmployeeID > 0
+        BEGIN
+            INSERT INTO @ProductsByEmployee (ID, ProductName, TotalPrice)
+            SELECT P.ProductID, P.ProductName, SUM(OD.UnitPrice * OD.Quantity) as TotalPrice
+            FROM Employees as E
+            JOIN Orders as O ON E.EmployeeID = O.EmployeeID
+            JOIN [Order Details] as OD ON OD.OrderID = O.OrderID
+            JOIN Products as P ON P.ProductID = OD.ProductID
+            WHERE E.EmployeeID = @EmployeeID
+            GROUP BY P.ProductID, P.ProductName
+        END
+    ELSE
+        BEGIN
+            INSERT INTO @ProductsByEmployee (ID, ProductName, TotalPrice)
+            VALUES (0, 'Invalid Employee ID', 0)
+        END
+
+    RETURN
+END
+
+-- Test
+SELECT * FROM ProductDetailsByEmployee(0)