Keys

Dangling Reference

A child value with no parent row fails the reference check.

highlighted = computed this step

Dangling reference

A child row dangles when its foreign-key value has no parent row.

missing parent\text{missing parent}

Find the missing parent

The dangling-reference count is 1, so the valid flag is no.

dangling=1\text{dangling}=1

Key examples are tiny finite table checks; SQL dialects, indexing, query planning, deferrable constraints, enforcement timing, performance, and product behavior are out of scope.

Dangling reference: parent tablecustomer_idname1Ada2Ben3Cy Dangling reference: child tableorder_idcustomer_idtotal101150104940 key columnsparent keychild foreign keycustomer_idcustomer_id child-to-parent linkschildRowchildValueparentRowsstatus01[0]match19[]missing duplicate parent keysvalueparentRowsnonenone dangling referenceschildRowvaluestatus19missing key factsfactvalueparentRowCount3childRowCount2duplicateParentKeyCount0referenceCount2danglingReferenceCount1parentKeyUniqueyesvalidnodeleteStatusnone

Read the status

The child-to-parent links table marks the unmatched child row as missing.

status missing\text{status missing}

Summary

The compiler refuses to treat a missing parent as a guess.

no guessed row\text{no guessed row}