Full Outer Joins

Honest by Construction

Expected FULL OUTER JOIN facts are assertions only.

highlighted = computed this step

Honest by construction

Expected FULL OUTER JOIN facts are assertions only.

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

Render checked rows

The guarded full outer join renders 7 output rows after recomputation.

checked rows=7\text{checked rows}=7

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

Honest by construction: left tableemp_idnamedept_id1Ada102Ben203Cy304DeeNULL Honest by construction: right tabledept_iddept_name10ops20eng20platform40legalNULLunknown candidate key matchesleftSourcerightSourceleftKeyrightKeymatched001010yes011020no021020no031040no0410NULLno102010no112020yes122020yes132040no1420NULLno203010no213020no223020no233040no2430NULLno30NULL10no31NULL20no32NULL20no33NULL40no34NULLNULLno FULL OUTER JOIN output rowsleft.emp_idleft.nameleft.dept_idright.dept_idright.dept_name1Ada1010ops2Ben2020eng2Ben2020platform3Cy30NULLNULL4DeeNULLNULLNULLNULLNULLNULL40legalNULLNULLNULLNULLunknown output row classificationclassleftSourcerightSourcerowmatched00[1, Ada, 10, 10, ops]matched11[2, Ben, 20, 20, eng]matched12[2, Ben, 20, 20, platform]left_only2NULL[3, Cy, 30, NULL, NULL]left_only3NULL[4, Dee, NULL, NULL, NULL]right_onlyNULL3[NULL, NULL, NULL, 40, legal]right_onlyNULL4[NULL, NULL, NULL, NULL, unknown] FULL OUTER JOIN factsfactvalueleftRowCount4rightRowCount5candidatePairCount20matchingPairCount3leftOnlyRowCount2rightOnlyRowCount2outputRowCount7duplicateMatchRows1nullKeyCandidatePairs8rowOrdermatched_left_source_then_left_only_then_right_only

Try to tamper

Wrong expected facts, derived sidecars, missing keys, duplicate columns, bools, floats, and unsafe cells fail closed.

tamper rejected\text{tamper rejected}

Summary

This book shows exact finite FULL OUTER JOIN behavior only.

scoped full outer model\text{scoped full outer model}