delete a value in a table with foreign key constraint code example

Example 1: how to remove foreign key constraint in sql

USE AdventureWorks2012;  
GO  
ALTER TABLE dbo.DocExe   
DROP CONSTRAINT FK_Column_B;   
GO

Example 2: on delete of foreign key delete corresponding rows in other table

ALTER TABLE ReferencingTable DROP 
   CONSTRAINT fk__ReferencingTable__MainTable;

ALTER TABLE ReferencingTable ADD 
   CONSTRAINT fk__ReferencingTable__MainTable 
      FOREIGN KEY (pk_col_1)
      REFERENCES MainTable (pk_col_1)
      ON DELETE CASCADE;

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