foreign key constraint sql server code example
Example 1: mysql add foreign key
CREATE TABLE tableName (
ID INT,
SomeEntityID INT,
PRIMARY KEY (ID),
FOREIGN KEY (SomeEntityID)
REFERENCES SomeEntityTable(ID)
ON DELETE CASCADE
);
ALTER TABLE
tableName
ADD
FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;
ALTER TABLE
tableName
ADD CONSTRAINT fk_name
FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;
Example 2: sql foreign key
CREATE TABLE users(
userId INT NOT NULL,
username VARCHAR(64) NOT NULL,
passwd VARCHAR(32) NOT NULL,
PRIMARY KEY(userId);
);
INSERT INTO users VALUES(1000,"Terry","Teabagface$2");
CREATE TABLE orders(
orderId INT NOT NULL,
orderDescription VARCHAR(255),
ordererId INT NOT NULL,
PRIMARY KEY(orderId),
FOREIGN KEY (ordererId) REFERENCES users(userId)
);
INSERT INTO orders VALUES(0001,"Goat p0rn Weekly",1000);
Example 3: 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;
Example 4: Cannot truncate a table referenced in a foreign key constraint (`video_clips`.`channel_clips`, CONSTRAINT `clips_fk` FOREIGN KEY (`clip_id`) REFERENCES `video_clips`.`clips` (`id`)) in sql]
SET FOREIGN_KEY_CHECKS = 0;
truncate table "yourTableName";
SET FOREIGN_KEY_CHECKS = 1;