Error 42830 (invalid_foreign_key) appears when a declared foreign key references columns that are not unique, not primary, or have incompatible data types or order.
PostgreSQL Error 42830 invalid_foreign_key arises when a FOREIGN KEY clause references columns that are non-unique or have mismatched data types. Correct the reference by pointing to a PRIMARY KEY or UNIQUE constraint with matching column order and types to resolve the issue.
PostgreSQL Error 42830
Error 42830 is raised at table creation or ALTER TABLE time when PostgreSQL cannot validate a FOREIGN KEY definition. The engine checks that the referenced columns exist, are unique, and match data types and order. A violation of any rule aborts the statement with condition name invalid_foreign_key.
Because the constraint never becomes valid, subsequent inserts or updates fail to compile.
Fixing the definition early prevents runtime surprises and preserves data integrity.
Referencing non-unique columns triggers 42830. PostgreSQL demands that the target columns have a PRIMARY KEY or UNIQUE constraint.
Data-type mismatch also causes failure. An INTEGER child column cannot safely reference a BIGINT parent column.
Column order matters.
If the child lists columns in a different sequence than the parent’s composite key, PostgreSQL sees an invalid mapping and raises the error.
Using an expression, excluded column, or partial index as the target also leads to invalid_foreign_key.
First, ensure the parent table exposes a PRIMARY KEY or UNIQUE constraint on the referenced columns.
Add or adjust the constraint if missing.
Second, confirm that the child table columns share identical data types and appear in the same order as the parent’s key.
Third, recreate or alter the foreign key with the corrected column list.
Validate the constraint to ensure it is accepted.
Scenario 1 – No UNIQUE constraint: Add a UNIQUE index to the parent, then re-run the ALTER TABLE on the child.
Scenario 2 – Type mismatch: Cast or change the child column type to match the parent, or vice versa, using ALTER TABLE ... ALTER COLUMN ...
TYPE.
Scenario 3 – Column order: Rewrite the FOREIGN KEY list so it matches the parent key’s column ordering.
Always define PRIMARY KEYs before adding foreign keys. Galaxy’s schema-aware autocomplete highlights columns with UNIQUE constraints, reducing mistakes.
Use identical data types for related columns. Stick to canonical IDs such as BIGINT everywhere.
Validate constraints after creation by running ALTER TABLE ...
VALIDATE CONSTRAINT to catch issues early in migration scripts.
23503 foreign_key_violation: Raised during DML when child rows reference missing parent rows. Fix by inserting the parent or deleting the orphan rows.
23502 not_null_violation: Occurs when inserting NULL into a NOT NULL column. Ensure all required columns are populated.
42P07 duplicate_table: Triggered when creating a table that already exists in the schema.
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It is a DDL error. PostgreSQL throws it while creating or altering tables, not during data modifications.
No. PostgreSQL must validate a foreign key at creation time. You can defer enforcement but only after the constraint is accepted.
No. Only data type, uniqueness, and order matter. Names may differ between parent and child.
Galaxy’s AI copilot auto-suggests valid parent keys and flags data-type mismatches before you run the DDL, preventing invalid_foreign_key errors.
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