Documentation

Comprehensive SQL reference from fundamentals to advanced topics. Each page includes syntax, real examples, common mistakes, and links to practice problems.

Fundamentals

SELECT, FROM, WHERE — the building blocks of every query

SELECT Statements

Retrieve data from tables

WHERE Clause

Filter rows with conditions

Operators

AND, OR, NOT, IN, BETWEEN, LIKE

ORDER BY

Sort your results

LIMIT & OFFSET

Paginate result sets

DISTINCT

Remove duplicate rows

Aggregations

Summarize data with grouping and aggregate functions

COUNT

Count rows and values

SUM & AVG

Calculate totals and averages

MIN & MAX

Find extreme values

GROUP BY

Group rows for aggregation

HAVING

Filter groups after aggregation

Joins

Combine data from multiple tables

INNER JOIN

Matching rows from both tables

LEFT JOIN

All rows from left, matching from right

RIGHT JOIN

All rows from right, matching from left

FULL OUTER JOIN

All rows from both tables

Self Join

Join a table to itself

CROSS JOIN

Cartesian product of two tables

Subqueries

Queries within queries for complex logic

Scalar Subqueries

Single value subqueries

Derived Tables

Subqueries in FROM clause

Correlated Subqueries

Row-by-row evaluation

EXISTS & NOT EXISTS

Test for row existence

Window Functions

Calculations across sets of rows related to the current row

ROW_NUMBER

Assign sequential numbers

RANK & DENSE_RANK

Rank with tie handling

LAG & LEAD

Access previous/next rows

Running Totals

Cumulative calculations

NTILE

Divide rows into buckets

Advanced

CTEs, CASE expressions, date functions, and more

Common Table Expressions

WITH clause for readable queries

Recursive CTEs

Hierarchical data traversal

CASE Expressions

Conditional logic in SQL

UNION & INTERSECT

Combine result sets

Date Functions

Work with dates and timestamps

String Functions

Text manipulation