Join output size

Worked examples, recomputed

Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.

• keys 7 (5 × 3) and 8 (2 × 1) → 17 rows from 11
• a key 10× oversized on both sides → 100× the work
• 3 orders × 2 tickets through one customer → 6 rows
• freight repeated per line: 70 instead of 30

Where it appears

Each mechanism states it in its own names. The general symbol each name stands for is shown with it.

• Query Processing

  Why can one question be answered by plans whose costs differ by a factor of ten thousand, and what does each operator force the engine to do?

  $$\sum _v{f}_R(v)\cdot f_S(v)$$

  Read it in place →

• Data Modeling

  What does one row mean, who is allowed to change that answer, and what breaks downstream when they do?

  $$\text{rows}=\sum _v{f}_{\text{orders}}(v)\cdot f_{\text{tickets}}(v)$$

  Read it in place →