CREATE TABLE `t1`  ( 
	`c1`	int(11) NULL,
	PRIMARY KEY(`c1`)
)
GO
CREATE TABLE `t2`  ( 
	`c1`	int(11) NULL 
	)
GO
ALTER TABLE `t2`
	ADD CONSTRAINT `fk`
	FOREIGN KEY(`c1`)
	REFERENCES `t1`(`c1`)

GO