Snippet Name: Enable_and_Disable_Constraints

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Created Date: 2025-06-16 13:12:45
Last Modified Date: 2025-05-31 10:31:42

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Title: Enable and Disable Constraints
Author: user
in SQL server, i want to disable all foreign key constraints int he database. i have seperate code to delete soem data, but after it is done, i need to re-enable any disabled foreign key constraints with CHECK

Author: ChatGPT
To disable all foreign key constraints in an SQL Server database, you can use dynamic SQL to generate and execute the necessary `ALTER TABLE` statements. Here is a script that disables all foreign key constraints in the database:

```sql
-- Disable all foreign key constraints
DECLARE @sql NVARCHAR(MAX) = N'';

SELECT @sql += 'ALTER TABLE ' + QUOTENAME(OBJECT_SCHEMA_NAME(parent_object_id)) + '.' + QUOTENAME(OBJECT_NAME(parent_object_id)) 
    + ' NOCHECK CONSTRAINT ' + QUOTENAME(name) + ';'
FROM sys.foreign_keys;

EXEC sp_executesql @sql;
```

After performing the required data deletion operations, you can re-enable and check all foreign key constraints using the following script:

```sql
-- Re-enable all foreign key constraints with CHECK
DECLARE @sql NVARCHAR(MAX) = N'';

SELECT @sql += 'ALTER TABLE ' + QUOTENAME(OBJECT_SCHEMA_NAME(parent_object_id)) + '.' + QUOTENAME(OBJECT_NAME(parent_object_id)) 
    + ' WITH CHECK CHECK CONSTRAINT ' + QUOTENAME(name) + ';'
FROM sys.foreign_keys;

EXEC sp_executesql @sql;
```

### Explanation:

1. **Disable Foreign Key Constraints**:
    - The script selects all foreign keys from the `sys.foreign_keys` system view.
    - It constructs `ALTER TABLE ... NOCHECK CONSTRAINT ...` statements to disable each foreign key constraint.
    - The `sp_executesql` stored procedure executes the dynamically constructed SQL statements.

2. **Re-enable and Check Foreign Key Constraints**:
    - Similar to the disable script, this script selects all foreign keys from the `sys.foreign_keys` system view.
    - It constructs `ALTER TABLE ... WITH CHECK CHECK CONSTRAINT ...` statements to re-enable and enforce each foreign key constraint.
    - The `sp_executesql` stored procedure executes the dynamically constructed SQL statements.

Ensure to run these scripts in the appropriate context where you have permissions to alter tables and constraints.