Help & Documentation

Everything you need to know to get the most out of SQL Interview Playground

Getting Started

1. Choose Your Difficulty Level

Start with Easy questions if you're new to SQL, or jump to Medium, Hard, or Expert based on your experience.

2. Review the Question

Each question includes a description, available tables, and sample data previews to help you understand the requirements.

3. Write Your SQL Query

Use the SQL editor to write your solution. The editor provides syntax highlighting, autocompletion, and error detection.

4. Test Your Solution

Click "Run Query" to execute your SQL and see if your results match the expected output.

SQL Editor Features

✨ Syntax Highlighting

SQL keywords, functions, and identifiers are color-coded for better readability.

🔍 Autocompletion

Press Ctrl+Space for intelligent suggestions of SQL keywords and functions.

📝 Line Numbers

Easy navigation with line numbers and error location indicators.

🌙 Dark Mode

Toggle between light and dark themes using the theme switcher in the navigation.

Common SQL Patterns

Basic SELECT

SELECT
  column1, column2
FROM
  table_name
WHERE
  condition;

INNER JOIN

SELECT
  a.column1, b.column2
FROM
  table_a a
JOIN
  table_b b ON a.id = b.a_id;

GROUP BY with Aggregation

SELECT
  department, COUNT(*) as emp_count
FROM
  employees
GROUP BY
  department;

Troubleshooting

❌ Query Failed to Execute

  • Check for syntax errors (missing semicolons, mismatched quotes)
  • Verify table and column names match the schema
  • Ensure proper JOIN conditions are specified
  • Check for reserved keyword conflicts

⚠️ Results Don't Match Expected Output

  • Check the ORDER BY clause - result order matters
  • Verify column names and aliases match exactly
  • Review filtering conditions (WHERE, HAVING clauses)
  • Ensure proper handling of NULL values

💡 Performance Tips

  • Use specific column names instead of SELECT *
  • Apply WHERE conditions early to filter data
  • Use appropriate JOIN types (INNER, LEFT, etc.)
  • Consider using EXISTS instead of IN for subqueries

Keyboard Shortcuts

Editor Shortcuts

AutocompletionCtrl + Space
FindCtrl + F
ReplaceCtrl + H
Comment LineCtrl + /

Navigation

Go to LineCtrl + G
Select AllCtrl + A
UndoCtrl + Z
RedoCtrl + Y

SQL Reference

Basic Operations

  • SELECT, FROM, WHERE
  • ORDER BY, LIMIT
  • DISTINCT, IN, LIKE
  • AND, OR, NOT

Joins

  • INNER JOIN
  • LEFT JOIN
  • RIGHT JOIN
  • FULL OUTER JOIN

Aggregation

  • COUNT, SUM, AVG
  • MIN, MAX
  • GROUP BY
  • HAVING

Advanced

  • Subqueries
  • Window Functions
  • CTEs (WITH)
  • UNION, INTERSECT

Window Functions

  • ROW_NUMBER()
  • RANK(), DENSE_RANK()
  • LAG(), LEAD()
  • PARTITION BY

String Functions

  • CONCAT, LENGTH
  • UPPER, LOWER
  • SUBSTRING, TRIM
  • REPLACE, LIKE

Ready to start practicing?

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