JOIN USING

NULL Keys Do Not Match

NULL keys do not match under the equality rule.

highlighted = computed this step

NULL keys do not match

A NULL key on either side does not match in this finite equality model.

NULL not equal\text{NULL not equal}

Read NULL candidates

The candidate grid has 8 pairs with at least one NULL key, and none are matches.

NULL key pairs=8\text{NULL key pairs}=8

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.

NULL keys do not match: left tableorder_idcustomer_idnote110new220rush320gift4NULLdraft NULL keys do not match: 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 NULL equality

Even NULL with NULL is not a key match here.

NULL not matched\text{NULL not matched}

Summary

NULL key rows are visible before they are dropped by the inner join.

visible drop\text{visible drop}