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Explain plan for SELECT

We need to give an example of explain select ... plan and describe its internals.

  1. We need to introduce SELECTION, PROJECTION and SCAN plan nodes (look at presentation from #412 (moved)). Keep in mind that PROJECTION must always be above SELECTION (optional).
  2. Need examples for each possible combination:
    • SCAN + PROJECTION: select a from t, select * from t
    • SCAN + SELECTION + PROJECTION: select a from t where a = 1
  3. Explain what distribution key means and how it helps us to reduce the amount of instances to query (part of #418 (moved))
Edited by Denis Smirnov