Data join explosion diagnosis calculator

Calculate join contribution [key,left count,right count,inner-join rows] and predicted inner-join row count with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use join contribution [key,left count,right count,inner-join rows] and predicted inner-join row count to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

JSON Left table key frequencies [key,count]
[["A",3],["B",1]]
JSON Right table key frequencies [key,count]
[["A",2],["C",4]]
Join contribution [key,left count,right count,inner-join rows]
[["A",3,2,6],["B",1,0,0],["C",0,4,0]]
Predicted inner-join row count
6
Many-to-many key IDs
["A"]

Try another scenario

JSON Left table key frequencies [key,count]
[["A",3],["B",1]]
JSON Right table key frequencies [key,count]
[["A",4],["B",1],["C",4]]
Join contribution [key,left count,right count,inner-join rows]
[["A",3,4,12],["B",1,1,1],["C",0,4,0]]
Predicted inner-join row count
13
Many-to-many key IDs
["A"]
Calculation method

Calculation method

Join contribution [key,left count,right count,inner-join rows]

For each exact key, multiply left and right frequency, absent count zero.

Predicted inner-join row count

Sum keywise frequency products.

Many-to-many key IDs

Keys whose left and right counts both exceed one.

Symbols and units
a
JSON Left table key frequencies [key,count]
b
JSON Right table key frequencies [key,count]

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Assumptions & limits

Assumptions & limits

  • Exact equality inner join only; null matching semantics must be encoded as explicit included/excluded keys. No SQL execution. Supported limits: All numeric inputs must be finite. Only the explicitly described mathematical scenario is supported.
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