Skip to content
CodeKruPro

Stage 8 of 11

SQL

Queries testers write, from SELECT to joins and data checks, run on a real database.

Start: Name and city of every department
  1. Not startedSELECT basicsChoosing columns and rows from one table.0/7
  2. Not startedFiltering and sortingWHERE conditions, LIKE, IN, BETWEEN, ORDER BY and LIMIT.0/10
  3. Not startedWorking with NULLIS NULL, COALESCE and how NULL changes comparisons and counts.0/8
  4. Not startedAggregate functionsCOUNT, SUM, AVG, MIN and MAX.0/8
  5. Not startedGROUP BY and HAVINGGrouping rows and filtering groups.0/8
  6. Not startedJoinsInner, left and self joins, and finding rows with no match.0/9
  7. Not startedSubqueriesQueries inside queries: IN, EXISTS and correlated subqueries.0/7
  8. Not startedNth highest and rankingSecond highest salary, top N per group and window functions.0/9
  9. Not startedUNION and set operationsUNION, UNION ALL, INTERSECT and EXCEPT.0/7
  10. Not startedCreating and changing data (DDL and DML)CREATE, ALTER, INSERT, UPDATE and DELETE, and the difference between DELETE, TRUNCATE and DROP.0/9
  11. Not startedKeys, constraints, indexes and transactionsPrimary and foreign keys, constraints, indexes and transactions.0/11
  12. Not startedData checks a tester writesDuplicates, orphans, missing values and comparing data after a change.0/11
Not startedNot startedIn progressIn progressSolvedSolvedPro+Pro+

The first 2 questions of each topic are free. Pro+ opens every question.