Database Design & Constraints
Verify normal forms, map key constraints (FK, PK, UNIQUE), and enforce referential check rules.
SQL Query Architecture & Optimization Guide
Database design and administration covers relational schema normalization (1NF through 3NF), primary and foreign key constraints, B-Tree and Hash indexing strategies, and query plan inspection using EXPLAIN ANALYZE.
Relational engines enforce uniqueness and foreign key integrity during write operations. During reads, the planner consults table statistics and index B-Trees to determine whether index scans or sequential scans minimize I/O cost.
Creating too many indexes slows down INSERT, UPDATE, and DELETE operations. Furthermore, composite indexes on (A, B) cannot satisfy queries filtering only on B without A (violating the leftmost prefix rule).
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Frequently Asked Questions on Database Design & Constraints
How does the leftmost prefix rule work for composite indexes?
A composite index on columns (A, B) can accelerate queries filtering on A alone or (A and B), but cannot be used for queries filtering on B alone without referencing A.
What is the difference between Clustered and Non-Clustered Indexes?
A Clustered Index determines the physical storage order of table records (one per table). A Non-Clustered Index is a separate B-Tree structure storing pointers back to the base table rows.
What is Third Normal Form (3NF) in database design?
A table is in 3NF if it satisfies 2NF and contains no transitive dependencies, meaning every non-key attribute depends solely on the primary key.