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Cheat Sheets / CS Theory
01.02 · Cheat sheet

DBMS

Keys, normalisation, ACID, isolation levels, locking, indexing, ER modelling and SQL command groups on one page.

3 min Cheat sheet Pro

The DBMS facts interviewers ask most, in one place.

Keys

  • Super key: any set of columns that identifies a row.
  • Candidate key: a minimal super key.
  • Primary key: the chosen candidate key. Unique and not null.
  • Alternate key: a candidate key that wasn’t chosen.
  • Foreign key: refers to the primary key of another table.
  • Composite key: a key made of two or more columns.
  • Unique key: values must be unique; NULLs are allowed.

Normal forms

FormRule
1NFAtomic values, no repeating groups
2NF1NF + no non-key column depends on part of a composite key
3NF2NF + no non-key column depends on another non-key column
BCNFFor every dependency X → Y, X is a super key

Denormalise on purpose to make reads faster (fewer joins).

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Inside: 9 sections.

  • Keys
  • Normal forms
  • ACID
  • Isolation levels
  • Concurrency control
  • Indexing
  • +3 more
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Item 2 of 12 · updated 2026-10-13