drop foreign key
ALTER TABLE table_name
DROP CONSTRAINT fk_name;drop foreign key
ALTER TABLE table_name
DROP CONSTRAINT fk_name;mysql add foreign key
-- On Create
CREATE TABLE tableName (
ID INT,
SomeEntityID INT,
PRIMARY KEY (ID),
FOREIGN KEY (SomeEntityID)
REFERENCES SomeEntityTable(ID)
ON DELETE CASCADE
);
-- On Alter, if the column already exists but has no FK
ALTER TABLE
tableName
ADD
FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;
-- Add FK with a specific name
-- On Alter, if the column already exists but has no FK
ALTER TABLE
tableName
ADD CONSTRAINT fk_name
FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;what is foreign key in sql
Foreign Key:
It is a column that comes from a different table and
using Foreign key tables are related each other
It is the primary key of another table
It can be duplicate or null for another tableCopyright © 2021 Codeinu
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