JOIN USING

Candidate Key Comparisons

Candidate pairs compare the USING key.

highlighted = computed this step

Candidate key comparisons

The compiler compares each left key with each right key.

candidate comparisons\text{candidate comparisons}

Read candidates

The candidate grid has 20 pairs and 5 matches.

matches=5\text{matches}=5

JOIN USING 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.

Candidate key comparisons: left tableorder_idcustomer_idnote110new220rush320gift4NULLdraft Candidate key comparisons: right tablecustomer_idnamenote10Adavip20Benstandard20Bennyduplicate30CyprospectNULLUnknownmissing candidate key comparisonsleftSourcerightSourceleftKeyrightKeymatched001010yes011020no021020no031030no0410NULLno102010no112020yes122020yes132030no1420NULLno202010no212020yes222020yes232030no2420NULLno30NULL10no31NULL20no32NULL20no33NULL30no34NULLNULLno JOIN USING output rowscustomer_idleft.order_idleft.noteright.nameright.note101newAdavip202rushBenstandard202rushBennyduplicate203giftBenstandard203giftBennyduplicate ON join contrast rowsleft.order_idleft.customer_idleft.noteright.customer_idright.nameright.note110new10Adavip220rush20Benstandard220rush20Bennyduplicate320gift20Benstandard320gift20Bennyduplicate JOIN USING factsfactvalueleftRowCount4rightRowCount5candidatePairCount20matchingPairCount5matchedLeftRows3duplicateMatchRows2nullKeyCandidatePairs8usingKeyAppearsOnceyesduplicateNonKeyNames[note]outputColumnCount5onOutputColumnCount6rowOrderleft_source_then_right_source

No hidden match

Each candidate row marks yes or no.

matched flag visible\text{matched flag visible}

Summary

Only non-NULL equal keys become output rows.

equal non NULL keys\text{equal non NULL keys}