SQL
Master SQL for database interviews and data analyst placements. JOINs, GROUP BY, subqueries, and the tricky edge cases that trip up most candidates.
SQL GROUP BY and HAVING
GROUP BY collapses rows sharing common values into summary rows; HAVING filters these groups after aggregation.
GROUP BY is tested in virtually every SQL interview. Understanding the WHERE vs HAVING distinction and what can appear in SELECT alongside GROUP BY is critical.
SQL JOINs
SQL JOINs combine rows from two or more tables based on a related column.
JOIN is the single most important SQL concept. Every database interview and most placement SQL rounds test JOIN understanding — especially the difference between INNER, LEFT, RIGHT, and FULL OUTER.
SQL Subqueries
A subquery is a query nested inside another query, used to compute intermediate results for the outer query.
Subqueries are essential for multi-step data retrieval. They appear frequently in placement SQL rounds, especially for 'find the max/min within a group' patterns.
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