JOIN USING

Same-Named Key Inputs

JOIN USING starts from same-named key columns.

highlighted = computed this step

Same-named key inputs

JOIN USING starts with a key column that has the same name on both sides.

same named key\text{same named key}

Read inputs

The left table has 4 rows; the right table has 5 rows.

left rows=4\text{left rows}=4

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.

Same-named key inputs: left tableorder_idcustomer_idnote110new220rush320gift4NULLdraft Same-named key inputs: 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

One key name

Both tables have a customer id key column in this pinned example.

USING key visible\text{USING key visible}

Summary

The shared key name lets the output show that key once.

key once later\text{key once later}