Joins (Deep Dive)
3 Topics
1
INNER JOIN
Matching rows between two or more tables using join conditions.
INNER JOIN is the most fundamental join type tested in SQL interviews — interviewers evaluate your understanding of join conditions, multi-table joins, join performance, and how INNER JOIN differs from outer joins in handling unmatched rows.
2
LEFT, RIGHT, and FULL JOINS
Preserving unmatched rows from one or both sides of a join.
Outer joins are a frequent interview topic — interviewers test whether you understand which side is preserved, how NULLs appear for unmatched rows, how to filter "orphans" with IS NULL, and the behavioral difference between LEFT JOIN and INNER JOIN when rows have no match.
3
SELF JOIN and CROSS JOIN
Joining a table to itself and generating cartesian product combinations.
SELF JOIN and CROSS JOIN are tested to evaluate understanding of hierarchical data modeling, recursive relationships, generating combinations, and knowing when a cartesian product is intentional versus a bug.