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Questions and Answers
ما هو الفرق بين char(10) و varchar(10)؟
ما هو الفرق بين char(10) و varchar(10)؟
ما هو الفرق بين create database و drop database؟
ما هو الفرق بين create database و drop database؟
create database عبارة عن عبارة SQL تستخدم لإنشاء قاعدة بيانات جديدة، بينما drop database عبارة عن عبارة SQL تستخدم لحذف قاعدة بيانات موجودة.
يمكن استخدام أكثر من كلمة رئيسية (Primary Key) في جدول واحد.
يمكن استخدام أكثر من كلمة رئيسية (Primary Key) في جدول واحد.
False
ما هو دور constraint في SQL؟
ما هو دور constraint في SQL؟
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ما هي أنماط constraint المعروفة في SQL؟
ما هي أنماط constraint المعروفة في SQL؟
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ما هو دور on update في constraint؟
ما هو دور on update في constraint؟
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ما هو الفرق بين select و retrieve في SQL؟
ما هو الفرق بين select و retrieve في SQL؟
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ما هو دور group by في SQL؟
ما هو دور group by في SQL؟
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تستخدم الدوال التجميعية Aggregate Functions مع group by clause.
تستخدم الدوال التجميعية Aggregate Functions مع group by clause.
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Study Notes
Database Design
- Database design involves several stages: analysis, entity-relationship diagrams (ER diagrams), schema, Data Definition Language (DDL), and Data Manipulation Language (DML).
- Analysis focuses on identifying entities (objects) and their attributes (characteristics).
- Relationships between entities are crucial; examples include 1:1, 1:M, and M:M relationships.
Attributes
- Key attributes are unique identifiers. Examples include student ID, serial number, and social security number.
- Composite attributes are composed of multiple parts. An address, for instance, might include street, city, and zip code
- Multi-valued attributes can hold multiple values for a single entity. Examples include phone numbers and email addresses.
- Derived attributes are calculated from other attributes. An example is the average grade of students.
Entity Types
- Strong entities exist independently. Examples include students and courses
- Weak entities depend on other entities. Examples include dependent in the employee relation, as they depend on the employee for existence
- Recursive relationships occur when an entity relates to itself. An example is the hierarchical structure of an employee supervisory relationship.
- Ternary relationships describe relationships between three entities. For example, the relationship between a supplier, a project, and an item.
Database Implementation
- Converting an ER diagram to a relational database schema involves mapping entities to tables.
- Attributes become columns and relationships become foreign keys.
SQL
- SQL (Structured Query Language) is used to manage and manipulate data in databases.
- DDL (Data Definition Language) commands are used to define tables, columns, and constraints.
- DML (Data Manipulation Language) commands are used to manipulate data within the database. These include insert, select, update, and delete statements.
Constraints
- Constraints are rules applied to data integrity and consistency. Common constraints include:
- Key constraints to ensure uniqueness.
-
not nullto prevent missing values. -
uniqueto prevent duplicate values. -
checkto enforce specific rules.
-
defaultvalue is used to set default values to columns.
Data Types
- Data types specify the kind of data a column can hold. Note variances between VARCHAR(length) and CHAR(length).
Additional Notes
- Database management systems (DBMS) use SQL to interact with databases.
- Common database systems include SQL Server
- Multiple relationships exist in database design.
- Proper constraints are essential to maintain data integrity.
- DDL commands are used to create, modify, and delete tables and columns.
- DML commands are used to insert, select, update, and delete data from tables.
- Foreign keys establish relationships between tables.
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Description
تتناول هذه المسابقة مراحل تصميم قواعد البيانات مثل التحليل، والرسوم البيانية للعلاقات الكيانية، ومخططات البيانات. ستختبر معرفتك بالخصائص والسمات لمختلف أنواع الكيانات وكذلك العلاقة بينها.
