Learn SQL with Real Code Examples

SQL provides declarative commands to interact with relational database systems (RDBMS).

Supports querying, filtering, aggregation, joins, and transactions.

Used across major RDBMS like MySQL, PostgreSQL, Oracle, SQL Server, and SQLite.

Enforces schema, data types, constraints, and relationships.

Enables both simple queries and complex analytical operations.

SELECT queries with filtering and ordering

INSERT, UPDATE, DELETE operations

JOINs (INNER, LEFT, RIGHT, FULL) and subqueries

GROUP BY, HAVING, and aggregate functions

Transactions and constraint enforcement

Database - container for related tables

Table - collection of rows with defined columns

Row/Record - single entry in a table

Column/Field - attribute of a table with data type

Primary/Foreign Keys - enforce uniqueness and relationships

Database instance

Schemas for logical separation

Tables representing entities

Views for reusable queries

Stored procedures/functions for business logic

Define schema: tables, columns, constraints

Insert initial data

Query and retrieve data using SELECT

Update or delete data as needed

Ensure transactions maintain consistency and integrity

Beginner: simple SELECT queries

Intermediate: joins, filtering, and aggregation

Advanced: complex nested queries, CTEs, and window functions

Expert: database optimization, indexing, and partitioning

Enterprise: multi-database transactional systems with replication and sharding

SQL vs NoSQL: SQL for structured data, NoSQL for flexible schema/unstructured data

MySQL vs PostgreSQL: MySQL widely used, PostgreSQL more advanced features

SQL vs GraphQL: SQL queries relational data, GraphQL queries API endpoints

SQL vs ORM query languages: SQL native and powerful, ORM abstracts complexity

SQL vs Excel: SQL handles large datasets efficiently, Excel for small-scale analysis

1970s - SQL developed at IBM

1986 - ANSI SQL standard established

1989 - SQL-89 standard

1992 - SQL-92 with expanded features

2025 - Latest SQL standards with JSON, analytical functions, and windowing support

RDBMS - Relational Database Management System

Table - structured collection of rows

Row/Record - single data entry

Column/Field - attribute with data type

Primary/Foreign Key - enforces relationships and uniqueness