INFO90002 Chap.6 SQL DDL, DML and Integrity

SQL DDL, DML and Integrity

SQL DDL, DML and Integrity turns table definition, constraints and insert update delete into executable reasoning. The chapter's practical target is to encode business rules at the strongest appropriate database boundary, so every explanation should connect syntax to program state, control flow and observable output.

Treat table definition as a precise program object, not a loose label.

Identify its value or responsibility before execution, then trace what can read it, change it or depend on it. This makes hidden state changes visible before they become debugging guesses.

Use constraints to explain the program's next move. Work through one representative input by hand and name the branch, iteration or call that follows.

If the trace cannot be stated, the code may run by accident rather than by understood design.

Bring in insert update delete as the test of structure.

Compare normal, boundary and invalid inputs; state the expected behaviour first; then use the mismatch between expectation and result to localise the defect.

For the application — encode business rules at the strongest appropriate database boundary — write the smallest complete example that exposes the rule.

Explain why it works, what would break it and how the program should signal or recover from that failure.

Before running a SQL DDL, DML and Integrity example, make a trace table with the important state before and after each operation. Include the value associated with table definition, the control decision governed by constraints and the output or object affected by insert update delete.

The table turns an unexplained result into a sequence that can be tested one transition at a time.

Test three inputs: an ordinary case, a boundary case and an invalid case. State the expected result for each before execution, then compare it with what the program actually does.

A useful test of constraints isolates one rule; a test that changes several conditions at once cannot tell you which condition caused the failure.

Practise explaining the solution without reading the code.

For INFO90002, name the data representation, the control flow, the responsibility of each function or class and the reason the chosen design supports encode business rules at the strongest appropriate database boundary.

This rehearsal is especially important when a written test or interview asks why the program works rather than whether it produces one correct output.

A complete SQL DDL, DML and Integrity response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to constraints, and use insert update delete to test the result.

The final sentence should answer the question actually asked rather than merely repeat the topic.

The controlling limit is specific: Application validation alone does not protect all database writers.

Keep that limit beside the worked example, because it separates a careful INFO90002 answer from one that sounds confident but claims more than the task or evidence supports.

For revision, retrieve table definition, constraints and insert update delete without notes, explain their relationship aloud, then complete a changed version of the application: encode business rules at the strongest appropriate database boundary.

Record the first point at which your reasoning fails and repair that move before attempting another case.

What this chapter covers

• 01

  table definition

• 02

  constraints

• 03

  insert update delete

• 04

  Applying table definition

• 05

  Limits of constraints and insert update delete

Worked example: SQL DDL, DML and Integrity

Key terms

DDL, DML and DCL (CREATE/DROP/ALTER vs SELECT/INSERT/UPDATE/DELETE vs GRANT/REVOKE)

DDL defines database structures with commands such as CREATE, ALTER and DROP; DML queries or changes data with SELECT, INSERT, UPDATE and DELETE; DCL manages privileges with GRANT and REVOKE. In this chapter, use the concept when you encode business rules at the strongest appropriate database boundary.

conceptual, logical and physical design (the database development lifecycle)

Conceptual design models business entities and relationships independently of technology, logical design translates them into a data model and constraints, and physical design specifies storage, indexes and implementation details. In this chapter, use the concept when you encode business rules at the strongest appropriate database boundary.

transactions, concurrency and locking

A transaction is a logical unit of database work that should satisfy ACID properties; concurrency control and locking coordinate simultaneous transactions to prevent inconsistent or lost updates. In this chapter, use the concept when you encode business rules at the strongest appropriate database boundary.

SQL DDL, DML and Integrity FAQ

Exam move

Reconstruct the relationship among table definition, constraints and insert update delete; complete the chapter application without notes; then test the result against this limit: Application validation alone does not protect all database writers.

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