DBMS Flashcards
Flip-card revision for DBMS — normalization, keys, transactions, indexing, and SQL fundamentals for C-CAT exam preparation and quick recall.
Can a Primary Key be NULL?
No, never — uniqueness and non-NULL are its two defining constraints
Difference between Super Key and Candidate Key
Every candidate key is a super key, but a candidate key is minimal — no redundant attributes
What does 1NF require?
Atomic values only, no repeating groups
What does 2NF eliminate?
Partial dependency — a non-key attribute depending on only part of a composite key
What does 3NF eliminate?
Transitive dependency — a non-key attribute depending on another non-key attribute
GRANT and REVOKE belong to which SQL category?
DCL (Data Control Language)
Which SQL category includes INSERT, UPDATE, DELETE?
DML (Data Manipulation Language)
Atomicity vs Durability — what's the difference?
Atomicity = all-or-nothing DURING execution. Durability = stays saved AFTER commit, survives crashes
How many clustered indexes can a table have?
Only 1 — it determines the physical storage order of the table's rows
In Two-Phase Locking, what happens right after the first lock release?
The transaction enters the shrinking phase and cannot acquire any new locks
What does a LEFT JOIN return?
All rows from the left table, with NULLs for right-table columns where there's no match
B+ Tree vs B-Tree — which do most real databases actually use for indexing?
B+ Tree — all data lives at the leaf level, and leaves are linked for efficient range scans
What is a derived attribute?
One computed from another attribute — e.g. Age from Date of Birth — not stored directly
What does a Foreign Key do?
References a Primary Key in another table, enforcing referential integrity between them
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