SQL-Levels-Explained

Explaining sql levels based on one meme:

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Level 0

• Concepts
  • ORMs
  • data types
  • foreign keys
  • indexes
• SQL: Just go through https://mode.com/sql-tutorial/
  • SELECT/INSERT/UPDATE/DELETE
    • SELECT DISTINCT
  • ORDER BY
  • GROUP BY
  • LIMIT/OFFSET
  • CREATE TABLE
  • JOIN

Level 1

• Concepts
  • ACID
  • transactions
  • keyset pagination
  • normal forms
  • computed columns
  • stored columns
  • inverted indexes
  • window functions
• SQL
  • outer joins
  • ORDER BY in aggregates
  • CTEs
  • query plans and EXPLAIN

Level 2

• Concepts
  • Connection pools
  • plan hints
  • cursors
  • MVCC garbage collection
  • recursive CTEs
  • LATERAL joins
• Insights
  • ORMs create bad queries: explanation needed
  • optimizers don't work without table statistics: explanation needed
  • there are no non-nullable types: explanation needed

Level 3

• Concepts
  • MERGE
  • COUNT(*) vs COUNT(1): https://svenweller.wordpress.com/2016/10/11/otn-apprecition-day-the-otn-forum/
  • isolation levels
  • zigzag join
  • grouping sets, cube, rollup
  • write skew
  • partial indexes
  • sharding
  • phantom reads
  • triggers
• Insights
  • serializable restarts require retry loops on all statements: explanation needed
  • generator functions zip when cross joined: explanation needed

Level 4

• Concepts
  • SELECT FOR UPDATE
  • denormalization
  • transaction contention
  • sargability
  • star schemas
  • utf8mb4
• Insights
  • Ascending Key Problem: explanation needed
  • Ambiguous network errors: explanation needed
  • NULLs in CHECK constraints are truthy: explanation needed

Level 5

• Concepts
  • DEFERRABLE INITIALLY IMMEDIATE
  • MATCH PARTIAL foreign keys
  • EXPLAIN approximates SELECT COUNT(*)
  • causual reverse
• Insights
  • TPCC requires wait times: explanation needed
  • cost models don't reflect reality: explanation needed
  • 'null'::jsonb IS NULL = false: explanation needed

Level 6

• Concepts
  • database cracking: explanation needed
  • learned indexes: explanation needed
  • XTID exhaustion: explanation needed
  • Worst Case Optimal Join: explanation needed
  • Volcano model: explanation needed
• Battle Scars
  • Vectorized doesn't mean SIMD: explanation needed
  • join ordering is NP hard: explanation needed
  • NULLs are equal in DISTINCT but inequal in UNIQUE: explanation needed

Level 7

• dee and dum: https://blog.jooq.org/creating-tables-dum-and-dee-in-postgresql/
• the Halloween problem: https://en.wikipedia.org/wiki/Halloween_Problem
• allballs: https://www.postgresql.org/message-id/24526.1106597936%40sss.pgh.pa.us
• fsyncgate: explanation needed
• Every SQL operator is actually a JOIN: explanation needed
• SERIAL is non-transactional: explanation needed
• NULL (?): explanation needed