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#0331
Next Login Date
MediumSQL24 min20 XP
Problem
Return user_id, login_date, and next_login_date for every login.
Why This Matters
SQL interviews usually test whether you can turn a business question into the right rows, grouping level, join type, and edge-case behavior.
Schema
logins(login_id INTEGER, user_id INTEGER, login_date TEXT)
Examples
Example 1
Inputuser 1 has Jan 1 and Jan 4 logins
OutputJan 1 next login is Jan 4
LEAD reads the next row in the user partition.
Constraints
- Return only the requested columns.
- Use deterministic ORDER BY when multiple rows are returned.
- Assume SQLite-compatible SQL unless the prompt states otherwise.
CodeSQL
Visible browser tests run here when available.
Testcases1 visible / 3 hidden categories
Core SQL case
Inputuser 1 has Jan 1 and Jan 4 logins
Expected[[1,"2026-01-01","2026-01-04"],[1,"2026-01-04",null],[2,"2026-01-02",null]]
LEAD reads the next row in the user partition.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks