Merge pull request #1978 from souvikpramanikgit/add-sqlviews

Add SQL Views

docs/languages/SQL/sql-33.md

@@ -0,0 +1,90 @@
+---
+id: sql-views
+sidebar_position: 33
+title: "SQL Views"
+sidebar_label: "SQL Views"
+description: "SQL Views are virtual tables that represent a saved query in the database."
+tags: [sql, dbms, database, views, virtual tables]
+---
+
+A **View** in SQL is a virtual table based on a result set of a `SELECT` query. Views can simplify complex queries, enhance security by limiting data access, and provide a more user-friendly way to access data.
+
+### Advantages of Views
+
+- **Simplicity**: Abstract complex queries, allowing easier access to data.
+- **Security**: Restrict access to specific data by allowing users to query a view instead of underlying tables.
+- **Data Consistency**: Ensure data consistency by allowing standardized queries to run on views instead of individual tables.
+
+### Syntax
+
+```sql
+CREATE VIEW view_name AS
+SELECT column1, column2, ...
+FROM table_name
+WHERE condition;
+```
+
+### Example
+
+**Example 1: Creating a Simple View**
+
+Create a view named CustomerView that displays only selected columns from the Customers table.
+
+```sql
+CREATE VIEW CustomerView AS
+SELECT CustomerID, CustomerName, Country
+FROM Customers;
+```
+
+To query data from this view:
+
+```sql
+SELECT * FROM CustomerView;
+```
+
+**Example 2: View with Join**
+
+Create a view that combines data from multiple tables to show order details.
+
+```sql
+CREATE VIEW OrderDetailsView AS
+SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate, Orders.Amount
+FROM Orders
+JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
+```
+
+**Example 3: Updating Data through a View**
+
+In some SQL databases, views can be updatable. This depends on database constraints and view complexity. Here’s an example of updating a view:
+
+```sql
+UPDATE CustomerView
+SET Country = 'USA'
+WHERE CustomerID = 1;
+```
+
+Note: Not all views are updatable. Complex views (e.g., those with joins, group functions) may not support updates.
+
+### Managing Views
+
+* **Modify a View:** Use CREATE OR REPLACE VIEW to modify an existing view without dropping it.
+
+```sql
+CREATE OR REPLACE VIEW CustomerView AS
+SELECT CustomerID, CustomerName
+FROM Customers
+WHERE Country = 'USA';
+```
+
+* **Delete a View:** Use DROP VIEW to remove a view from the database.
+
+```sql
+DROP VIEW view_name;
+```
+
+**Notes :**
+* Virtual Table: A view doesn’t store data; it only stores the SQL query that defines it.
+* Read-Only Views: Some views are read-only depending on complexity and database constraints.
+* Permissions: Views can provide restricted data access to specific users without exposing full tables.
+
+SQL Views are powerful tools that enhance database usability, security, and data management by abstracting and simplifying access to underlying tables.