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> Documentation for Manipulating Constraints

# Manipulating Constraints

Constraints could be added or deleted using following syntax:

```sql theme={null}
ALTER TABLE [db].name [ON CLUSTER cluster] ADD CONSTRAINT [IF NOT EXISTS] constraint_name CHECK expression;
ALTER TABLE [db].name [ON CLUSTER cluster] DROP CONSTRAINT [IF EXISTS] constraint_name;
```

See more on [constraints](/reference/statements/create/table#constraints).

Queries will add or remove metadata about constraints from table, so they are processed immediately.

<Tip>
  Constraint check **will not be executed** on existing data if it was added.
</Tip>

All changes on replicated tables are broadcast to ZooKeeper and will be applied on other replicas as well.