Explain the statement that relational algebra operators can be composed. Why is the ability to compose operators important
1 answer:
You might be interested in
Answer:
/******************************
Both of the queries below will work in SQL Server
Oracle
******************************/
SELECT o.OrderID, c.CompanyName, e.FirstName, e.LastName
FROM Orders o
JOIN Employees e ON (e.EmployeeID = o.EmployeeID)
JOIN Customers c ON (c.CustomerID = o.CustomerID)
WHERE o.ShippedDate > o.RequiredDate AND o.OrderDate > '1-Jan-1998'
ORDER BY c.CompanyName;
/******************************
MySQL
******************************/
SELECT o.OrderID, c.CompanyName, e.FirstName, e.LastName
FROM Orders o
JOIN Employees e ON (e.EmployeeID = o.EmployeeID)
JOIN Customers c ON (c.CustomerID = o.CustomerID)
WHERE o.ShippedDate > o.RequiredDate AND o.OrderDate > '1998-01-01'
ORDER BY c.CompanyName;
