alter table add foreign key mysql
ALTER TABLE orders
ADD
FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;alter table add foreign key mysql
ALTER TABLE orders
ADD
FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;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;fk in insert mysql
INSERT INTO joke(joke_text, joke_date, author_id)
VALUES (‘Humpty Dumpty had a great fall.’, ‘1899–03–13’,
(SELECT id FROM author WHERE author_name = ‘Famous Anthony’));foreign key mySql
CREATE TABLE parent (
id INT NOT NULL,
PRIMARY KEY (id)
) ENGINE=INNODB;
CREATE TABLE child (
id INT,
parent_id INT,
INDEX par_ind (parent_id),
FOREIGN KEY (parent_id)
REFERENCES parent(id)
ON DELETE CASCADE
) ENGINE=INNODB;alter table add column and foreign key mysql
ALTER TABLE database.table
ADD COLUMN columnname INT DEFAULT(1),
ADD FOREIGN KEY fk_name(fk_column) REFERENCES reftable(refcolumn) ON DELETE CASCADE;Copyright © 2021 Codeinu
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