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HubUnit 1 — Introduction to DBMS & Entity-Relationship ModelAdvantages and Disadvantages of DBMSAggregationCharacteristics of DBMSData IndependenceData ModelsDatabase Users and AdministratorsDBMS LanguagesER DiagramsEntity-Relationship ER ModelIntroduction to DBMSKeys in DBMSRelationships and CardinalitySchema and InstanceSpecialization and GeneralizationUnit 1 Summary — Introduction to DBMS & ER ModelThree-Level Architecture ANSI/SPARC ArchitectureWeak Entity SetUnit 2 — Relational Model & SQLConstraints in SQLCursorsDCL and TCL CommandsDDL CommandsDML CommandsDomain Relational Calculus DRCFunctions and Stored ProceduresJoins in SQLNested Queries SubqueriesRelational AlgebraRelational CalculusRelational ModelSQL IntroductionUnit 2 Summary — Relational Model & SQLTriggers in SQLTuple Relational Calculus TRCViews in SQLArmstrong's Axioms & Closure of AttributesBoyce-Codd Normal Form BCNFClosure of AttributesDependency PreservationFifth Normal Form 5NFFirst Normal Form 1NFFourth Normal Form 4NFFunctional DependencyLossless DecompositionMultivalued DependencyNormal Forms — OverviewNormalization — IntroductionSecond Normal Form 2NFUnit 3 Summary — NormalizationThird Normal Form 3NFUnit 4 — Transaction Management & Concurrency ControlACID PropertiesCheckpointsConcurrency Control & SerializabilityDeadlock in DBMSLock-Based Protocols & Two-Phase LockingLog-Based RecoveryRecovery SystemSerializabilityShadow PagingUnit 4 Summary — Transaction Management & Concurrency ControlTimestamp-Based ProtocolTransaction ManagementTransaction StatesTwo-Phase Locking 2PLUnit 5 — Storage & IndexingB+ TreeB-TreeCost EstimationDynamic HashingFile OrganizationHashing TechniquesIndexing — IntroductionMulti-Level IndexingQuery OptimizationQuery ProcessingSingle-Level IndexingStatic HashingUnit 5 Summary — Storage & IndexingUnit 6 — Advanced Topics in DBMSBig Data and DBMSCloud DatabaseData MiningData WarehouseDatabase SecurityDistributed DatabaseDistributed Query ProcessingDistributed DBMS Architecture, Fragmentation & ReplicationMongoDB — IntroductionNoSQL DatabaseReplication in Distributed DatabasesUnit 6 Summary — Advanced Topics in DBMSViva Voce — DBMSImportant Viva Questions — DBMSInterview Questions — DBMSViva Answers — DBMSDBMS Multiple Choice Questions MCQsDBMS Lab Programs
Second Normal Form 2NF
Last Updated : 21 May, 2026
A relation is in Second Normal Form 2NF if:
Unit 3122 words6 headingsExamples included
Definition
A relation is in Second Normal Form (2NF) if:
- It is in 1NF, AND
- Every non-prime attribute is fully functionally dependent on the entire primary key (no partial dependencies)
A partial dependency occurs when a non-key attribute depends on only a part of a composite primary key. 2NF is automatically satisfied if the primary key has only one attribute.
Identifying Partial Dependencies
| Relation | OrderDetail(OrderID, ProductID, ProductName, Quantity, UnitPrice) |
| Primary Key | (OrderID, ProductID) |
| (OrderID, ProductID) | Quantity ← Full ✓ |
| ProductID | ProductName ← PARTIAL ✗ (depends on part of PK) |
| ProductID | UnitPrice ← PARTIAL ✗ |
Decomposition to 2NF
Remove each partial dependency into a separate table:
| Step 1 | Identify partial FDs: |
| ProductID | ProductName, UnitPrice |
| Step 2 | Create new table for each partial dependency: |
| Step 3 | Remove those attributes from original (keep FK): |
| FK: ProductID | Product.ProductID |
Another Example
| PK | (SID, CID) |
| SID | SName, SEmail (student info depends only on SID) |
| CID | CName, Credits (course info depends only on CID) |
| (SID, CID) | Grade (grade needs both — FULL ✓) |
Visual: Before and After 2NF
BEFORE (Partial Dependencies)
┌──────────────────────────────────────────┐
│ StudentCourse(SID, CID, SName, Grade) │
│ ↑ ↑ │
│ Composite PK │
│ SID ──────────────────► SName (✗ partial)│
│ (SID,CID) ────────────► Grade (✓ full) │
└──────────────────────────────────────────┘
AFTER (2NF)
Student(SID, SName)
Enrollment(SID, CID, Grade)
Key Points
- 2NF applies only when there is a composite primary key
- Single-attribute PK → relation in 1NF is automatically in 2NF
- After 2NF, transitive dependencies may still exist (fixed in 3NF)
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Second Normal Form 2NF.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this DBMS topic.
Search Terms
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Unit 3Fifth Normal Form 5NFA relation R is in Fifth Normal Form 5NF — also called Project-Join Normal Form PJ/NF — if, for every non-trivial join dependency R1, R2, ..., Rn in R:Unit 3First Normal Form 1NFA relation is in First Normal Form 1NF if:Unit 3Fourth Normal Form 4NFA relation R is in Fourth Normal Form 4NF if, for every non-trivial multivalued dependency X →→ Y in R:Unit 3Third Normal Form 3NFA relation is in Third Normal Form 3NF if:Unit 3Normal Forms — OverviewUnit 3Boyce-Codd Normal Form BCNFA relation R is in BCNF Boyce-Codd Normal Form if, for every non-trivial functional dependency X → Y in R: