Sep 08, 2026: Add and drop hybrid table constraints online (General availability)¶

With this release, you can add and drop UNIQUE and FOREIGN KEY constraints on an existing hybrid table by using ALTER TABLE. Previously, you had to define these constraints when you created the table, so adding a foreign key to a table that was already serving a workload meant recreating and reloading the table.

The change is an online operation. Snowflake builds the index that backs the constraint in the background, and the table stays available for SELECT and DML statements while the build runs:

ALTER TABLE player ADD CONSTRAINT fk_player_team
  FOREIGN KEY (team_id) REFERENCES team (team_id);

Because the build runs in the background, the ALTER TABLE statement returns before the constraint is fully in place. Use SHOW INDEXES to track the build. The status column reports BUILD IN PROGRESS while the index is building and ACTIVE when the constraint is ready.

Adding a constraint also validates the rows that are already in the table. If some of them violate the new constraint, the ALTER TABLE statement still succeeds and the background build reports a status of BUILD VALIDATION FAILURE. A constraint in that state still enforces every new write. Only the rows that were already in the table remain unvalidated. To recover, drop the constraint, correct the offending rows, and add the constraint again.

For more information, see Add and drop constraints on an existing hybrid table.