SQL
What is SQL: Databases, DBMS and RDBMS
SQL is the declarative language used to define and query relational data. Start here to see what a database, a DBMS and an RDBMS actually are.
SQL
A complete SQL path: fundamentals, DDL and DML, querying, joins, subqueries, CTEs, window functions, design, indexing, transactions, performance and security.
91 notes in 31 topics
Topics in SQL
SQL Basics 6
DDL 3
DML 3
SELECT 3
WHERE 3
Functions 4
NULL and Logic 2
Aggregate Functions 2
GROUP BY 3
JOIN 5
Subqueries 4
Set Operations 2
CTEs 2
Constraints 3
Keys 2
Relationships 2
Database Design 2
Normalisation 3
Views 2
Window Functions 4
Advanced SQL 6
Procedures and Functions 2
Triggers 2
Temporary Tables 2
Transactions 2
Isolation and Locking 3
Indexes 3
Query Performance 3
SQL Security 2
SQL Dialects 2
Practical SQL 4
Notes
SQL
The Relational Model: Tables, Rows, Columns and Schemas
Tables hold typed columns and unordered rows, schemas hold tables, and every value obeys the type its column declares.
SQL
SQL Syntax, Keywords, Identifiers and Comments
How a SQL statement is built: clause order, keywords versus identifiers, quoting rules, statement terminators and the two comment styles.
SQL
SQL Data Types Explained
Numeric, string, date and boolean types across the major dialects, and how to pick the type that stops bad data at the door.
SQL
SQL Operators and Expressions
Arithmetic, comparison, logical, string and set operators, how precedence works, and where an expression may legally appear.
SQL
The Sample Database Used in This Path
Two small schemas - a company HR database and a shop sales database - used by every example in this SQL path. Create them once and follow along.
SQL
CREATE: Databases, Schemas and Tables
CREATE defines the objects data lives in. Learn CREATE DATABASE, CREATE SCHEMA and CREATE TABLE, with column definitions and inline constraints.
SQL
ALTER TABLE: Adding, Modifying and Removing Columns
ALTER changes a table that already holds data. Add and drop columns, change types, set defaults and manage constraints without losing rows.
SQL
DROP, TRUNCATE and DELETE Compared
Three ways to remove data, with very different consequences. Learn what each one destroys, what can be rolled back and what resets identity counters.
SQL
INSERT: Single Row, Multi Row and INSERT SELECT
Every way to put rows into a table: explicit column lists, multi row VALUES, INSERT ... SELECT, defaults and handling duplicate keys.
SQL
UPDATE: Conditional and Multi Column Changes
UPDATE changes existing rows. Learn multi column updates, conditional logic with CASE, updates driven by a join and how to check the blast radius firs...
SQL
DELETE and Safe Data Modification
DELETE removes rows permanently. Learn targeted deletes, deleting through a join, soft deletes and the habits that stop a one line mistake becoming an...