• 前言
  There are a couple of ways to add constraints to restrict the values in the database. This article is about how to define a foreign key constraint and a check constraint in two ways.
• Table T1

CREATE TABLE T1 ( PID INT PRIMARY KEY,score INT,ISMINORITY VARCHAR(1) );

• Table T2
  we are going to define a fk constraint and a check constraint on T2
  
  • the inline way

CREATE TABLE T2 ( PID INT CONSTRAINT FK_PID REFERENCES T1(PID),ISMINORITY VARCHAR(1) CHECK(ISMINORITY IN ('N','Y')) );

• the out-of-line way

CREATE TABLE T2 ( PID INT,ISMINORITY VARCHAR(1),CONSTRAINT FK_PID FOREIGN KEY (PID) REFERENCES T1(PID),CONSTRAINT CHECK_ISMINORITY CHECK(ISMINORITY IN ('N','Y')) );