To query a user's mobile phone and WeChat number, the following SQL statement can be used.

HackerRank isn’t just a random collection of problems; they’ve organized their SQL section pretty well. You can find challenges that cover everything from basic SELECT statements to more involved ...

previousTab: WITH ranked_tabs AS ( SELECT id, timestamp, LAG(id) OVER (ORDER BY timestamp) as prev_tab_id FROM tab ) SELECT prev_tab_id FROM ranked_tabs WHERE id ...