Join Multiplication

Honest by Construction

Expected join facts are assertions only.

highlighted = computed this step

Honest by construction

Expected join-multiplication facts are assertions only.

compiler is source of truth\text{compiler is source of truth}

Render checked rows

The guarded join renders 3 rows after recomputation.

checked rows=3\text{checked rows}=3

Inner-join examples are tiny finite-table transforms; SQL dialect completeness, type coercion, optimizer behavior, execution cost, indexing, and database-product claims are out of scope.

Honest by construction: left tablecustomer_idname1Ada2Ben3CyNULLNoKey Honest by construction: right tablecustomer_idorder_iditem1101book1102pen2103bag4104lampNULL105mystery candidate row pairsleftSourcerightSourceleftKeyrightKeymatched00[1][1]yes01[1][1]yes02[1][2]no03[1][4]no04[1][NULL]no10[2][1]no11[2][1]no12[2][2]yes13[2][4]no14[2][NULL]no20[3][1]no21[3][1]no22[3][2]no23[3][4]no24[3][NULL]no30[NULL][1]no31[NULL][1]no32[NULL][2]no33[NULL][4]no34[NULL][NULL]no inner join rowsleft.customer_idleft.nameright.customer_idright.order_idright.item1Ada1101book1Ada1102pen2Ben2103bag inner join factsfactvalueleftRowCount4rightRowCount5candidatePairCount20matchingPairCount3unmatchedLeftRows2unmatchedRightRows2joinRowCount3keyColumnCount1nullKeyMatches0rowOrderleft_source_then_right_source

Try to tamper

Wrong expected facts, derived sidecars, missing keys, bools, and floats fail closed.

tamper rejected\text{tamper rejected}

Summary

This book shows exact finite inner-join multiplication only.

scoped join model\text{scoped join model}