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DBMS → Introduction to DBMS 33

To count questions per assignment_id and q_level in one query
SELECT assignment_id,q_level,COUNT(*) as cnt FROM questions GROUP BY assignment_id,q_level
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$table->foreignId('assignment_id')->constrained() creates
UNSIGNED BIGINT column PLUS FK constraint referencing assignments.id
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MERGE statement (SQL:2003) performs
INSERT UPDATE or DELETE based on match condition (UPSERT)
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To add composite index on (assignment_id, q_level) in Laravel migration
$table->index(['assignment_id','q_level'])
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Which SQL finds duplicate right_answer_id values in questions?
SELECT right_answer_id,COUNT(*) FROM questions GROUP BY right_answer_id HAVING COUNT(*)>1
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To get correct answer text when right_answer_id='option_b' for question id=1
SELECT option_b FROM questions WHERE id=1
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Eloquent query to get hard questions for assignment 1 that are not deleted
Question::where('q_level',3)->where('assignment_id',1)->where('is_deleted',0)->get()
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solution column in questions table contains
Full explanation/solution text for the question
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$table->enum('right_answer_id',['option_a','option_b','option_c','option_d','option_e']) creates
ENUM allowing only specified values
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option_e=NULL in questions table means
Question has only 4 options (no 5th option needed)
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created_at and updated_at in questions table are managed by
Eloquent automatic timestamp management ($timestamps=true by default)
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Which command adds CHECK constraint on q_level after table creation?
ALTER TABLE questions ADD CONSTRAINT chk_level CHECK (q_level BETWEEN 1 AND 3)
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To bulk insert 2000 questions efficiently without memory issues
DB::table()->insert(array_of_2000_arrays) - single bulk INSERT statement
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Which SQL gets questions for multiple assignments (1, 2, 3)?
DB::table('questions')->whereIn('assignment_id',[1,2,3])->get()
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Database design process order is
ER Model (conceptual) → Normalize (logical) → Migrate (physical implementation)
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To retrieve the right answer option text dynamically in SQL for any question
SELECT CASE right_answer_id WHEN 'option_a' THEN option_a WHEN 'option_b' THEN option_b WHEN 'option_c' THEN option_c WHEN 'option_d' THEN option_d ELSE option_e END as answer FROM questions WHERE id=1
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Which SQL removes all questions for a specific assignment and resets auto-increment?
UPDATE questions SET is_deleted=1 WHERE assignment_id=1 (soft delete preferred)
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In ARIES, losers (uncommitted at crash) require which recovery action?
UNDO - their incomplete changes must be reversed
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B+tree with height h requires how many I/Os for point query?
h+1 I/Os (h for tree traversal + 1 to fetch actual record)
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SQL injection is prevented by
Using parameterized queries (prepared statements) and input validation
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Principle of Least Privilege means
Grant ONLY minimum permissions needed for each user's tasks
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TDE (Transparent Data Encryption) protects
Data at rest by encrypting database files on disk
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RBAC means
Access based on assigned roles - permissions granted to roles, users assigned roles
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Database auditing records
ALL database activity (who did what, when, from where)
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Data masking replaces
Sensitive real data with realistic-looking but fictitious data for non-production use
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Data warehouse is characterized by
Subject-oriented, integrated, time-variant, non-volatile collection for decision support
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OLAP is optimized for
Complex analytical queries on large historical datasets
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Star schema fact table contains
Numeric measures + foreign keys to dimension tables
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ETL stands for
Extract Transform Load
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CAP theorem: during network partition choose between
Consistency OR Availability (cannot guarantee both)
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Sharding distributes
Table rows across multiple database servers based on a shard key
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NoSQL database best for social graph traversal
Graph database (Neo4j, Neptune)
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Recursive CTE requires
BASE CASE (anchor member) AND RECURSIVE CASE
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DBMS → Normalization 1

Normalization and Laravel migrations are related because
Migrations implement the normalized schema design in version-controlled PHP code
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DBMS → Transactions 1

In ARIES, winners (committed transactions at crash) require which recovery action?
REDO - their changes must be reapplied to ensure durability
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DBMS → Joins 1

Which join algorithm is best when inner table has index on join attribute?
Index nested-loop join (uses index to find matching rows rapidly)
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DBMS → Views 2

Materialized view differs from regular view because
It physically stores query results and can be refreshed periodically
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WITH CHECK OPTION on updatable view ensures
Updates through view MUST satisfy view's WHERE condition
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DBMS → PL/SQL 2

INSTEAD OF trigger on a view
Intercepts DML on views and executes custom logic replacing the standard DML
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Stored procedures improve security by
Allowing users to call procedure without direct table access (execute-only permission)
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