Backend Developer
SQL questions
38 questions on SQL for backend developers, easiest first.
Easy 19
- Stopping SQL injectioneasy
- Purpose of a database indexeasy
- Rows returned by a LEFT JOINeasy
- What a foreign key enforceseasy
- Atomicity in a money transfereasy
- COUNT and AVG with NULLseasy
- Filtering grouped resultseasy
- Duplicate emails despite a checkeasy
- What EXPLAIN tells youeasy
- Database user for the appeasy
- Building SQL from user inputeasy
- WHERE column = NULL finds nothingeasy
- COUNT(*) versus COUNT(column)easy
- Storing order times for two countrieseasy
- Rows come back in a new ordereasy
- Checking if any rows existeasy
- Which year is a leap yeareasy
- Month number in new Dateeasy
- Converting Dubai time to India timeeasy
Medium 14
- The N+1 query problemmedium
- Isolation levels and dirty readsmedium
- Offset or cursor paginationmedium
- Composite index column ordermedium
- Optimistic lock update hits 0 rowsmedium
- Index ignored for lower(email)medium
- Page view counter loses countsmedium
- Insert or update in one statementmedium
- Importing 100,000 rows slowlymedium
- Rows skipped with created_at cursorsmedium
- Joining two lists in memorymedium
- Adding one month to 31 Januarymedium
- Day count off by a fractionmedium
- Where NULLs go in PostgreSQL ORDER BYmedium