THE NUMBERS, EXPLAINED
How to use this calculator.
Enter the union of keys, using zero for absent keys; null matching follows your preprocessing policy. Counts are key frequencies, not raw records.
Start with your inputs
Enter left rows per aligned key (counts), right rows per aligned key (counts). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Left rows per aligned key (counts) | 2,3,0 |
| Right rows per aligned key (counts) | 4,0,5 |
A worked example
With the example inputs above, inner join rows (count) is 8. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Inner join rows (count) | 8 |
| Left join rows (count) | 11 |
| Full outer join rows (count) | 16 |
How this is calculated
Inner join rows (count)
Multiply left and right frequencies for every key and sum.
Left join rows (count)
Each left row matches the right count or emits one unmatched row.
Full outer join rows (count)
Use products for matched keys and original counts for unmatched keys.
Symbols and units
- a
- Left rows per aligned key (counts)
- b
- Right rows per aligned key (counts)
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions and limits
Enter the union of keys, using zero for absent keys; null matching follows your preprocessing policy. Counts are key frequencies, not raw records.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Inner join rows (count); Left join rows (count); Full outer join rows (count). The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Enter the union of keys, using zero for absent keys; null matching follows your preprocessing policy. Counts are key frequencies, not raw records.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Further reading
PostgreSQL Table Expressions — Joined Tables ↗
Background reading; this does not imply endorsement or independent review of SumFizz.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
Read the quality report →