Table Rules

The rules governing tables in a relational database are essential for maintaining data integrity and consistency. These rules help ensure that the data is organized and stored in a structured manner and that relationships between different tables are properly defined. Here are some of the key rules governing tables:

Unique Rows: Each row in a table must be unique. This means that no two rows in the table can have exactly the same values for all columns. Tables usually have a primary key, which is a column or set of columns that uniquely identifies each row.
Columns and Data Types: Each column in a table must have a unique name, and each column must have a specified data type that defines the type of data that can be stored in it (e.g., integer, string, date, etc.).
No Duplicate Columns: A table should not have duplicate column names. Each column name must be unique within the table.
No Ordering: In a relational database, the order of rows in a table should not have any inherent meaning. Data should be stored without any specific order, and the desired order should be achieved using the ORDER BY clause in SQL queries.
Referential Integrity: Tables can have relationships with each other through foreign keys. The referential integrity rule ensures that the relationships between tables are maintained. This means that a foreign key value in one table must match a primary key value in another table or be set to NULL.
Constraints: Tables can have various constraints applied to them to enforce specific rules. For example, NOT NULL constraint ensures that a column must have a value, UNIQUE constraint ensures that a column or set of columns must have unique values, and CHECK constraint allows you to define custom conditions that the data in a column must satisfy.
Atomicity: In database transactions, the rule of atomicity ensures that either all the changes made in a transaction are applied, or none of them are applied. This ensures that the database remains in a consistent state.
Consistency: The data stored in a table must be consistent with the defined data types and constraints. Data that does not meet the defined rules cannot be inserted into the table.
Isolation: Isolation ensures that the changes made in one transaction are not visible to other transactions until the changes are committed. This prevents conflicts and data inconsistencies.
Durability: Once a transaction is committed, its changes are permanent and survive any subsequent failures, ensuring the durability of the data.

These rules, collectively known as the rules of the relational model, form the foundation of relational database systems and help ensure data integrity and reliability. Adhering to these rules allows developers and users to efficiently store, query, and manage data in a structured and predictable manner.