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What a foreign-key cascade deletes
A foreign key is declared on the referencing, or child, table and points to a referenced, or parent, table. With ON DELETE CASCADE, deleting a referenced parent row causes matching rows in the child table to be deleted. It does not mean deleting a child row deletes its parent. The action applies along the relationship declared by the constraint, not according to table names or application conventions. See the PostgreSQL constraints documentation and SQL Server’s primary and foreign key documentation.
A child row removed by one cascade may itself be referenced by other tables. Those relationships can trigger further actions, so the total impact depends on both the deployed schema and the particular parent rows selected.
Audit the delete in six steps
1. Fix the target scope
Record the database and schema, fully qualified parent table, exact WHERE predicate, and the parent key values it selects. Confirm the intended parent-row count independently, and check that your connection is pointed at the intended environment. Audit the same predicate you intend to execute; a broader delete can reach a different cascade graph in practice because it selects different keys.
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2. Inventory every incoming foreign key
For each constraint referencing the parent, record its name and schema, child and parent tables, ordered child-to-parent column mapping, delete action, and relevant enforcement, validation, or deferrability status when the engine exposes it. Constraint names may not be unique across the database, so identify each constraint by its schema and table as well as its name.
For a composite foreign key, use every column in the declared key mapping and preserve its order. Matching on only one column can produce incorrect row estimates. Catalog and metadata interfaces differ by engine: PostgreSQL records the relationship in pg_constraint; MySQL provides foreign-key metadata through INFORMATION_SCHEMA; SQLite provides PRAGMA foreign_key_list. The engine-specific starting points are described below.
3. Trace the full action graph
Map each parent-to-child relationship and label it with the actual delete action. Follow child tables onward wherever deleting their rows can cause further row deletion, especially through another CASCADE relationship. Check self-references and cycles under the rules of the database engine in use.
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Do not ignore other actions while tracing. SET NULL and SET DEFAULT change child key values rather than deleting those rows; NO ACTION or RESTRICT may prevent the parent delete while references remain. The precise support and checking behavior depend on the engine and constraint configuration.
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For each selected parent key, count matching child rows using the complete foreign-key mapping. Continue the calculation along downstream cascade edges. Report direct parent rows and each affected table separately, distinguishing rows deleted from rows updated by SET NULL or SET DEFAULT. Counts describe the data visible to the query when it runs; changes by other transactions can make them stale before execution.
Indexing child-side referencing columns can affect the cost of finding matching rows, but it does not change the referential action. PostgreSQL notes that indexing referencing columns is often useful for foreign-key checks in its constraints documentation.
5. Review triggers and enforcement
Inspect delete triggers on the parent and every table that may be affected. Trigger behavior can add effects beyond the rows described by the foreign-key graph. In SQL Server, cascading referential actions occur before affected-table AFTER DELETE triggers, and the order across multiple cascade chains can be unspecified; do not assume that timing or ordering applies to other engines. Consult the SQL Server documentation and verify the rules for your own engine.
Check whether constraints are enabled, enforced, or validated where those states exist. For SQLite, inspect PRAGMA foreign_keys on the same connection that will run the delete: enforcement is connection-specific, and changing the setting within a transaction is a no-op. PRAGMA foreign_key_check reports existing foreign-key violations; it is not a preview of which rows a particular delete would affect. See the SQLite foreign-key documentation.
6. Rehearse and verify deliberately
Where the engine and execution context support a reliable rollback, rehearse the exact target selection and delete on a test copy or in a controlled transaction, inspect the effects, and roll back the rehearsal. This can validate the workflow, but it does not replace a current backup, a restore plan, trigger review, or coordination with concurrent writers. Before production execution, repeat the target predicate and confirm the selected scope. Afterward, verify expected counts and application invariants.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Engine-specific places to inspect
These are starting points, not portable SQL recipes. Adapt table filters, permissions, partition handling, and catalog details to the deployed engine and version.
| Engine and version | Inspection starting point | Details to verify |
|---|---|---|
| PostgreSQL 18 | pg_constraint |
conrelid identifies the referencing table; confrelid identifies the referenced table; conkey and confkey hold child and parent columns; confdeltype encodes the delete action: a no action, r restrict, c cascade, n set null, and d set default. Also review condeferrable, condeferred, conenforced, and convalidated. See PostgreSQL’s pg_constraint catalog reference. |
| MySQL 8.4 | Foreign-key definitions and INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS |
Inspect the metadata’s ON DELETE attribute and verify storage-engine limitations for the server in use. The cited metadata documentation is under the MySQL 26.7 manual path, so check its exact columns against your server version. See MySQL 8.4 foreign-key documentation and MySQL’s REFERENTIAL_CONSTRAINTS reference. |
| SQL Server | Catalog metadata for foreign-key constraints | Inspect each constraint’s delete referential action in the catalog for the deployed SQL Server version. Review the documented actions and trigger behavior in Microsoft’s primary and foreign key documentation. |
| SQLite | PRAGMA foreign_key_list(table_name) |
Inspect declared foreign keys and their actions; check PRAGMA foreign_keys on the executing connection and use PRAGMA foreign_key_check to find violations. See SQLite’s foreign-key documentation. |
Interpret actions and timing carefully
NO ACTION and RESTRICT are not identical in timing across all engines. PostgreSQL permits deferred checking for NO ACTION in applicable deferrable constraints, whereas RESTRICT is not deferred. SQLite documents that RESTRICT raises an error immediately even when the constraint is deferred. Check the deployed engine’s rules in the PostgreSQL constraints documentation and SQLite foreign-key documentation.
SET NULL requires the affected child columns to allow nulls. SET DEFAULT relies on defaults that still satisfy referential integrity. Either action can fail if the resulting key values violate the schema’s requirements. See the SQL Server documentation and PostgreSQL constraints documentation.
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ON DELETE CASCADE is a row-level foreign-key action. PostgreSQL’s DROP ... CASCADE is a separate DDL operation that removes dependent database objects. It is not a preview or execution method for cascading row deletion. See PostgreSQL’s dependency documentation.
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