MSDN Documentation

SQL is a standard language for managing and manipulating databases. It's used to communicate with a database. SQL is a declarative language, meaning you tell the database what you want to do, and it figures out how to do it.

Key uses of SQL include:

• Querying data
• Inserting data
• Updating data
• Deleting data
• Creating and modifying database structures

Databases and Tables

A database is an organized collection of data. Within a database, data is typically stored in tables. A table is a collection of related data entries organized in a row-and-column format.

Columns and Rows

Each column in a table represents a specific attribute (e.g., 'CustomerID', 'FirstName'). Each row represents a single record or entry (e.g., a specific customer's details).

Primary Keys

A primary key is a column (or a set of columns) that uniquely identifies each row in a table. It ensures that no two rows have the same key value.

Foreign Keys

A foreign key is a column that establishes a link between two tables. It is a column in one table that refers to the primary key in another table, enforcing referential integrity.

SELECT: Retrieving Data

The SELECT statement is used to query the database and retrieve data from one or more tables.

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Example: Get all customer names and emails from the 'Customers' table.

SELECT FirstName, LastName, Email
FROM Customers;

INSERT: Adding Data

The INSERT INTO statement is used to add new records into a table.

INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);

Example: Add a new customer.

INSERT INTO Customers (FirstName, LastName, Email)
VALUES ('Jane', 'Doe', 'jane.doe@example.com');

UPDATE: Modifying Data

The UPDATE statement is used to modify existing records in a table.

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Example: Update the email for a customer named 'Jane Doe'.

UPDATE Customers
SET Email = 'jane.d@newdomain.com'
WHERE FirstName = 'Jane' AND LastName = 'Doe';

DELETE: Removing Data

The DELETE FROM statement is used to remove existing records from a table.

DELETE FROM table_name
WHERE condition;

Example: Delete a customer named 'Jane Doe'.

DELETE FROM Customers
WHERE FirstName = 'Jane' AND LastName = 'Doe';

Caution: Omitting the WHERE clause will delete ALL records from the table.