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databases.md

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Databases

Questions:

  • What are relational databases?
  • What are base operations for relations?
  • What are integrity and consistency?
  • What is ACID?
  • What is projection?
  • What is SELECT operation? Can we use returned value of SELECT as new ordinary table?
  • What are the next parts of SELECT operation: LIMIT, OFFSET, ORDER BY, GROUP BY?
  • How can you group rules in WHERE block?
  • What is JOIN operation? What are the differences between INNER, LEFT, RIGHT and FULL OUTER JOIN?
  • What are INSERT, UPDATE and DELETE operations? What data can be returned as results for such operations?
  • What is CAP theorem?
    • Does it work in real world?
    • What combination of CAP guarantees is not encountered in practice?
  • What are indexes?
    • How do indexes impact the effectiveness of queries?
    • What are the pros and cons of adding an index?
  • What are Views in Postgresql?
  • What are Sequences in Postgresql?
  • What is VACUUM operation in Postgresql?
  • What is the EXPLAIN command?
    • What do ANALYZE and BUFFERS add to command?
    • Why expected cost and actual results can differ?
    • Why do EXPLAIN results have tree structure and what are the nodes?
    • Why cost and time parts of nodes have range structure? What is a start and what is an end?
    • What are Seq, Index, Index Only and Bitmap Scans?
      • How do planner choices impact the computer resources consumption?
      • When Seq Scan would be the best choice?
    • How are Sort, Limit and HashAggregate described in EXPLAIN output?
    • What are Nested Loop, Merge Join and Hash Join?
      • What is the most effective operation?
      • Should you trust planner choices 100 percent of the times?
    • What do Result and Materialize in EXPLAIN mean?
  • Why count(*) is usually faster than count(specific_row) and SELECT reltuples FROM pg_class is even faster?

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