DBMS Topics
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
SQL Introduction
Last Updated : 21 May, 2026
SQL Structured Query Language is the standard language for interacting with relational databases. It allows users to define, manipulate, and control data in a relational
Unit 2366 words13 headingsTables includedExamples included
What is SQL?
SQL (Structured Query Language) is the standard language for interacting with relational databases. It allows users to define, manipulate, and control data in a relational database system.
SQL was developed at IBM by Donald Chamberlin and Raymond Boyce in the early 1970s (originally called SEQUEL). It became an ANSI standard in 1986 and an ISO standard in 1987.
History of SQL
| Year | Milestone |
|---|---|
| 1970 | E.F. Codd proposes the relational model |
| 1974 | SEQUEL developed at IBM (later renamed SQL) |
| 1979 | Oracle releases first commercial SQL database |
| 1986 | SQL-86: First ANSI/ISO SQL standard |
| 1989 | SQL-89 (minor revision) |
| 1992 | SQL-92 (SQL2) — major update, widely supported |
| 1999 | SQL-99 (SQL3) — added procedural features, triggers |
| 2003 | SQL:2003 — added XML features, window functions |
| 2011 | SQL:2011 — temporal data support |
| 2016 | SQL:2016 — JSON support |
| 2023 | SQL:2023 — property graph queries |
SQL vs. Relational Algebra/Calculus
| Relational Algebra | Procedural | How to get data |
| Relational Calculus | Declarative | What data to get |
| SQL | Declarative | Based on calculus, with procedural extensions |
SQL is relationally complete — any query expressible in relational algebra can be expressed in SQL.
Categories of SQL Commands
| DDL | CREATE, ALTER, DROP, TRUNCATE, RENAME |
| DML | SELECT, INSERT, UPDATE, DELETE |
| DCL | GRANT, REVOKE |
| TCL | COMMIT, ROLLBACK, SAVEPOINT |
SQL Data Types
Numeric Types
| Type | Description | Example |
|---|---|---|
| INT / INTEGER | Whole numbers | 42, -10 |
| BIGINT | Large integers | 9999999999 |
| SMALLINT | Small integers | 1-100 |
| DECIMAL(p, s) | Fixed precision | 9.99 |
| FLOAT / DOUBLE | Floating point | 3.14159 |
String Types
| Type | Description |
|---|---|
| CHAR(n) | Fixed-length string (padded with spaces) |
| VARCHAR(n) | Variable-length string (up to n characters) |
| TEXT | Large text (no length limit) |
Date and Time Types
| Type | Description | Example |
|---|---|---|
| DATE | Date only | '2024-01-15' |
| TIME | Time only | '14:30:00' |
| DATETIME | Date and time | '2024-01-15 14:30:00' |
| TIMESTAMP | Date+time with timezone | Automatic recording |
Other Types
| Type | Description |
|---|---|
| BOOLEAN | TRUE / FALSE |
| BLOB | Binary large object (images, files) |
| ENUM | One value from a predefined list |
Basic SQL Query Structure
SELECT column1, column2, ... -- Which columns to return
FROM table_name -- Source table(s)
JOIN other_table ON condition -- Join with another table
WHERE condition -- Filter rows
GROUP BY column -- Group rows
HAVING group_condition -- Filter groups
ORDER BY column [ASC | DESC] -- Sort results
LIMIT n -- Limit rows returned;
Query Execution Order (Logical)
1FROM / JOIN
2WHERE
3GROUP BY
4HAVING
5SELECT
6DISTINCT
7ORDER BY
8LIMIT
Note: This is the logical order (how SQL thinks), not necessarily the physical execution order chosen by the optimizer.
A Simple Complete Example
sql exampleWoHoTech
-- Create a table
CREATE TABLE Student (
student_id INT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
dept VARCHAR(50),
gpa DECIMAL(3, 2)
);
-- Insert data
INSERT INTO Student VALUES (1, 'Alice', 'CS', 9.2);
INSERT INTO Student VALUES (2, 'Bob', 'Math', 8.5);
INSERT INTO Student VALUES (3, 'Carol', 'CS', 9.5);
-- Query data
SELECT name, gpa
FROM Student
WHERE dept = 'CS'
ORDER BY gpa DESC;
-- Result:
-- +-------+-----+
-- | name | gpa |
-- +-------+-----+
-- | Carol | 9.5 |
-- | Alice | 9.2 |
-- +-------+-----+SQL vs. Other Languages
| Feature | SQL | Python/Java |
|---|---|---|
| Paradigm | Declarative | Imperative |
| Specifies | WHAT to get | HOW to get it |
| Set-based | Yes (works on sets) | No (loop-based) |
| Built for | Data management | General purpose |
| Learning curve | Low (English-like) | Medium-High |
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for SQL Introduction.
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Unit 2Unit 2 — Relational Model & SQLThis unit covers the formal foundations of relational databases and the Structured Query Language SQL. Starting from the mathematical basis of relational algebra and calcUnit 2Constraints in SQLConstraints are rules applied to table columns that restrict the type of data that can be inserted or updated. They enforce data integrity at the database level — indepenUnit 2CursorsA cursor is a database object that allows row-by-row processing of query results inside a stored procedure or PL/SQL block. While SQL naturally operates on sets of rows, Unit 2DCL and TCL CommandsDCL commands control access and permissions to database objects. They manage security by defining who can do what.Unit 2DDL CommandsData Definition Language DDL commands are used to define, modify, and remove database objects such as tables, indexes, views, and schemas. DDL commands affect the structuUnit 2DML CommandsData Manipulation Language DML commands are used to manipulate the data stored in database tables. DML operates on the instance rows/data, not the schema.