SELECT * FROM users: Select all columns from a table. | WHERE age > 18: Filter rows. | ORDER BY created_at DESC: Sort results.

INNER JOIN: Returns records that have matching values in both tables. | LEFT JOIN: Returns all records from the left table, and the matched records from the right table. | RIGHT JOIN: Returns all records from the right table, and the matched records from the left table.

SQL Cheatsheet

Q: PostgreSQL JSONB

Modern Postgres allows semi-structured data. -- Select a value from a JSON column SELECT data->>'name' FROM events;

Essential SQL commands, with a focus on modern PostgreSQL features. From basic queries to advanced data types.

When This Cheatsheet Helps Most

Use this page when you need to inspect production-like data quickly, verify joins, group records into reports, or debug JSON-heavy schemas in PostgreSQL without jumping between many docs pages.

Basics

Key / Code	Description
SELECT * FROM users	Select all columns from a table.
WHERE age > 18	Filter rows.
ORDER BY created_at DESC	Sort results.
LIMIT 10 OFFSET 5	Pagination.

Joins

Key / Code	Description
INNER JOIN	Returns records that have matching values in both tables.
LEFT JOIN	Returns all records from the left table, and the matched records from the right table.
RIGHT JOIN	Returns all records from the right table, and the matched records from the left table.
FULL OUTER JOIN	Returns all records when there is a match in either left or right table.

PostgreSQL JSONB

Modern Postgres allows semi-structured data.

-- Select a value from a JSON column
SELECT data->>'name' FROM events;

-- Filter by JSON value
SELECT * FROM events WHERE data->>'status' = 'completed';

Common Table Expressions (CTE)

Use `WITH` to create temporary result sets. Makes complex queries readable.

WITH regional_sales AS (
    SELECT region, SUM(amount) as total_sales
    FROM orders
    GROUP BY region
)
SELECT * FROM regional_sales WHERE total_sales > 10000;

Common SQL Mistakes

Frequent mistakes include forgetting the join condition, filtering after aggregation instead of before it, and assuming NULL behaves like an empty string or zero. Those errors usually produce results that look plausible but are wrong.

SQL formatter and minifier

Clean up large queries before sharing them in reviews, debugging sessions, or docs.

JSONPath queries for nested data

Helpful when your data mixes relational tables with nested JSON documents.

Latency targets for query performance

Use these thresholds when deciding whether a query or report is fast enough.

Regex patterns for text filtering

Useful for preprocessing, validating, or cleaning text before it reaches SQL.

Knowledge is power.