مفاهيم SQL العامة

General SQL Concepts

• SQL (Structured Query Language) is a specialized programming language for database management.
• SQL is used to manage data within databases.
• SQL is categorized into Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), and Transaction Control Language (TCL).

Data Definition Language (DDL)

• DDL commands are used to define, modify, and create the structure of a database.
• DDL is used to create databases and tables.

Data Manipulation Language (DML)

• DML commands are used for data manipulation such as insertion, updating, deletion, and retrieval of data.
• Operations like insert, update, delete, can be performed on data within a database.

Data Control Language (DCL)

• DCL commands control access permissions to database content.

Transaction Control Language (TCL)

• TCL statements control transactions.

SQL Syntax

• Semicolons (;) are used to terminate SQL statements.
• Commas (,) separate values within a list.
• Column names containing spaces are enclosed in square brackets ([ ]).

Data Constraints

• NOT NULL Constraint: Prevents empty values in a column.
• UNIQUE Constraint: Ensures unique entries in a column.

Creating a Database

• The general format for creating a database is CREATE DATABASE database_name.

Creating a Table

• The general format for creating a table is CREATE TABLE table_name and includes defining the columns and their data types.

Other Important Concepts

• SELECT statement: Retrieve data.
• FROM clause: Indicates the table that is the source of the data in the SELECT clause.
• WHERE clause: Filters rows in the SELECT statement based on a condition.
• GROUP BY clause: Groups rows that have the same values in one or more columns.