Sector file // sql

SQLDECODED.

Joins, indexes & queries

82 Questions56.3k Views3.4k Upvotes
15 easy51 med16 hard
0 of 82 solvedUp next: What is the difference between a primary key and a foreign key?

Easy

1 question

What is the logical order of execution of a SQL query?

DSA · 1.1k views

Medium

10 questions

Top-N per group with RANK() OVER (PARTITION BY) — how do you get top 2 per department without collapsing rows?

DSA · 1.2k views

What is a subquery and what is a correlated subquery?

DSA · 1.2k views

What is the difference between COUNT(*), COUNT(col), and COUNT(DISTINCT col)?

DSA · 967 views

What is the difference between EXISTS and IN?

DSA · 762 views

What is a CTE (Common Table Expression)?

DSA · 732 views

How do you update a table based on another table?

DSA · 718 views

How do you delete duplicate rows but keep one?

DSA · 592 views

What is the difference between NOT IN and NOT EXISTS when NULLs are involved?

DSA · 585 views

Hard

2 questions

What is a LATERAL join?

DSA · 970 views

LATERAL vs Window Function vs Correlated Subquery for top-N per group — which scales when?

System Design · 221 views

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