Database concepts and RDBMS
SELECT statements and WHERE clause
Filtering with comparison and logical operators
Sorting with ORDER BY
LIMIT and DISTINCT keywords
Understanding table relationships
INNER JOIN for matching records
LEFT, RIGHT, and FULL OUTER JOIN
CROSS JOIN and self-joins
Join performance optimization
Aggregate functions (COUNT, SUM, AVG, MIN, MAX)
GROUP BY for data summarization
HAVING clause for filtered aggregations
Multiple grouping columns
CASE statements for conditional logic
Subqueries (scalar, row, table)
Common Table Expressions (CTEs)
Window functions (ROW_NUMBER, RANK, LAG, LEAD)
Date and string manipulation
UNION and UNION ALL