Can you explain the consistency principle (C) from the ACID model and its significance for database transactions?

The Consistency principle from the ACID model guarantees that after a transaction is executed, the database remains in a correct state, satisfying all specified rules and constraints (for example, data integrity, foreign key constraints, uniqueness, etc.).

This means that a transaction should transform the database from one valid state to another. If the transaction violates the rules, it is rolled back, and the database reverts to the previous consistent state.

Implications for transactions:

• Ensures data integrity.
• Prevents the appearance of incorrect or contradictory data.
• Allows developers to be confident that after a successful transaction, the data complies with business rules.

Example: if in a banking system, money is transferred from one account to another — the transaction must either be fully completed (deduct money from one account and deposit it into another), or not executed at all, to prevent balance discrepancies.