Databases & CRUD Overview

What is a Database?

Structured (or semi/unstructured) data store accessed through a DBMS.

Types

Relational (SQL Server, MySQL, PostgreSQL)
NoSQL (Document, Key-Value, Column, Graph)
Cloud Managed (Azure SQL, AWS RDS)
Distributed / Sharded

Core Terminology

Term	Meaning
Table	Structured set of rows
Column	Named attribute / field
Row	Record instance
Primary Key	Unique identifier per row
Foreign Key	Referential link to PK in another table
Index	Lookup structure for fast search

Keys Overview

Primary, Foreign, Unique, Candidate, Composite, Super, Alternate.

SQL Command Groups

Group	Purpose	Examples
DDL	Define schema	CREATE, ALTER, DROP
DML	Manipulate data	INSERT, SELECT, UPDATE, DELETE
DCL	Permissions	GRANT, REVOKE
TCL	Transactions	COMMIT, ROLLBACK

CRUD Mapping

Operation	SQL	C# (Pseudo)
Create	INSERT	context.Add(entity)
Read	SELECT	context.Entities.Where(…)
Update	UPDATE	modify entity then Save
Delete	DELETE	context.Remove(entity)

ADO.NET Essentials

Namespace: System.Data.SqlClient (legacy) / Microsoft.Data.SqlClient (newer).

Typical Pattern:

using var conn = new SqlConnection(connectionString);
await conn.OpenAsync();
using var cmd = new SqlCommand("SELECT Id, Name FROM Students", conn);
using var reader = await cmd.ExecuteReaderAsync();
while (await reader.ReadAsync())
{
    int id = reader.GetInt32(0);
    string name = reader.GetString(1);
}

Sample Connection String

Server=localhost;Database=School;Trusted_Connection=True;TrustServerCertificate=True;

Learning Path

Understand CRUD conceptually (see in-memory sample)
Translate operations to SQL
Use ADO.NET / ORM (e.g., EF Core) for real persistence

Next Steps

Add EF Core sample & WinForms grid binding (future roadmap).