主键 PRIMARY KEY;
外键 REFERENCES;
检查约束 CHECK()
CREATE TABLE Orders ( order_num INTEGER NOT NULL PRIMARY KEY, order_date DETETION NOT NULL CHECK(quantity > 0), cust_id CHAR(10) NOT NULL REFERENCES customers (cust_id) );
ALTER TABLE Ordrs ADD CONSTRAINT FOREIGN KEY (cust_id) REFERENCES Customers (cust_id)
索引
CREATE INDEX prod_name_ind ON Products (prod_name);