is a virtual table that represents data from one or more than one database table. You can select data from single or multiple tables based on the
Access databases don't natively support SQL views. You'll need to use a "true" relational database to explore views, such as SQL Server and its copy of Northwind.
SQL statement creates a view. The simple format of the
statement is as
CREATE VIEW viewname AS selectstatement
The following CREATE VIEW statement creates myView with records as a result of SELECT myName FROM myTable :
CREATE VIEW myView AS SELECT myName FROM myTable
The following two CREATE VIEW statements create the View1 view and the View2 view from the Orders table based on different criteria:
CREATE VIEW "View1" AS SELECT OrderID, OrderDate, ShippedDate FROM Orders WHERE (Freight < 10) CREATE VIEW "View2" AS SELECT OrderID, OrderDate, ShippedDate FROM Orders WHERE (Freight > 1000)
You can also create views by selecting data from multiple tables. For example, the following view selects data from the Products and Categories tables. By using views this way, you can
CREATE VIEW "Products by Category" AS SELECT Categories.CategoryName, Products.ProductName, Products.QuantityPerUnit, Products.UnitsInStock, Products.Discontinued FROM Categories INNER JOIN Products ON Categories.CategoryID = Products.CategoryID WHERE Products.Discontinued <> 1 ORDER BY Categories.CategoryName, Products.ProductName
You may have
Most of today's databases support Extensible Markup Language (XML). In SQL Server, for example, you can execute SQL queries to return results as XML rather than standard rowsets. You can execute these queries directly or from within stored procedures. To retrieve results directly, you use the FOR XML clause of the SELECT statement. Within the FOR XML clause, you specify one of three XML modes: RAW , AUTO , or EXPLICIT . (You can also work with XML data in Access, Oracle, MySQL, and other databases, but the techniques vary.)
For example, this SQL Server SELECT statement retrieves information from the Customers and Orders tables in the Northwind database:
SELECT Customers.CustomerID, ContactName, CompanyName, Orders.CustomerID, OrderDate FROM Customers, Orders WHERE Customers.CustomerID = Orders.CustomerID AND (Customers.CustomerID = "NALFKI" OR Customers.CustomerID = "NXYZAA") ORDER BY Customers.CustomerID FOR XML AUTO
SQL injection is the process of using SQL queries and failing because of invalid
string str = "SELECT * FROM Table WHERE
Name='" + TextBox1.Text + "'";
Now, what happens when Amie O'Donell enters her name in TextBox1? The execution of the SQL query will fail because of invalid SQL syntax. You have to be careful when building and executing direct SQL queries. You can simply avoid this by checking if the user input has an invalid character in it.
Another common scenario is when the database server is expecting a number value and the user enters a string value or vice versa. This could lead to a failure if you don't have a check in the code. For example, you could use the ToString method to make sure the input is a valid query (using the Convert class to convert from one data type to another).