Problems
Callback's own problems and the LeetCode questions companies have been asking, in one place — pick a category, then filter by company, frequency, status, difficulty, topic, and language.
SQL & Data · Writers create new versions instead of overwriting, so readers see a consistent snapshot without blocking writers.
SQL & Data · LSM buffers writes in memory and merges sorted files later; a B-tree updates in place for steadier reads.
SQL & Data · Rows suit point lookups and transactions; columns suit scans and aggregates and compress far better.
SQL & Data · Operators process batches of column values instead of one row at a time, cutting interpretation overhead and using CPU caches well.
SQL & Data · Record the change durably before applying it, so a crash can be replayed.
SQL & Data · Read committed, repeatable read, snapshot, serializable — know which anomaly each permits.
SQL & Data · Database storage, independent compute warehouses, and a cloud services layer — a hybrid of shared-disk and shared-nothing.
SQL & Data · Immutable 50–500 MB columnar chunks created automatically, with per-column metadata that lets queries skip them.
SQL & Data · A window frame of six preceding rows is right only when every day has a row; fill the calendar first.
Extract Fields From a JSON Column
SQL & Data · Path into the document for scalars, cast them explicitly, and flatten arrays into rows before aggregating.