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25 lines
770 B
Markdown
25 lines
770 B
Markdown
---
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slug: /en/sql-reference/statements/alter/constraint
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sidebar_position: 43
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sidebar_label: CONSTRAINT
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---
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# Manipulating Constraints
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Constraints could be added or deleted using following syntax:
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``` sql
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ALTER TABLE [db].name [ON CLUSTER cluster] ADD CONSTRAINT constraint_name CHECK expression;
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ALTER TABLE [db].name [ON CLUSTER cluster] DROP CONSTRAINT constraint_name;
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```
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See more on [constraints](../../../sql-reference/statements/create/table.md#constraints).
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Queries will add or remove metadata about constraints from table, so they are processed immediately.
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:::tip
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Constraint check **will not be executed** on existing data if it was added.
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:::
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All changes on replicated tables are broadcasted to ZooKeeper and will be applied on other replicas as well.
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