32. Which CREATE TABLE statement is valid? A. CREATE TABLE ord_details         (ord_no NUMBER(2) PRIMARY KEY,  item_no NUMBER(3) PRIMARY KEY,  ord_date DATE NOT NULL); B. CREATE TABLE ord_details         (ord_no NUMBER(2) UNIQUE, NOT NULL,  item_no NUMBER(3),  ord_date DATE DEFAULT SYSDATE NOT NULL); C. CREATE TABLE ord_details         (ord_no NUMBER(2) ,  item_no NUMBER(3),  ord_date DATE DEFAULT NOT NULL,  CONSTRAINT ord_uq UNIQUE (ord_no),  CONSTRAINT ord_pk PRIMARY KEY (ord_no)); D. CREATE TABLE ord_details  (ord_no NUMBER(2),  item_no NUMBER(3),  ord_date DATE DEFAULT SYSDATE NOT NULL,  CONSTRAINT ord_pk PRIMARY KEY (ord_no, item_no)); Answer: D

答案解析

A，一個表只有一個主鍵。A錯。 [email protected]> CREATE TABLE ord_details   2  (ord_no NUMBER(2) PRIMARY KEY,   3  item_no NUMBER(3) PRIMARY KEY,   4  ord_date DATE NOT NULL); item_no NUMBER(3) PRIMARY KEY,                   * ERROR at line 3: ORA-02260: table can have only one primary key B答案：UNIQUE, NOT NULL之間不要逗號，列級約束不要逗號，B錯

[email protected]> CREATE TABLE ord_details           2  (ord_no NUMBER(2) UNIQUE, NOT NULL,   3  item_no NUMBER(3),    4  ord_date DATE DEFAULT SYSDATE NOT NULL); (ord_no NUMBER(2) UNIQUE, NOT NULL,                           * ERROR at line 2: ORA-00904: : invalid identifier 逗號去掉可以建立，成功 [email protected]> CREATE TABLE ord_details   2  (ord_no NUMBER(2) UNIQUE NOT NULL,   3  item_no NUMBER(3),   4  ord_date DATE DEFAULT SYSDATE NOT NULL); Table created. C答案，兩處錯誤，一個DEFAULT 後面沒有指定預設值，一個是ord_no列的UNIQUE 和PRIMARY KEY [email protected]> CREATE TABLE ord_details           2  (ord_no NUMBER(2) ,   3  item_no NUMBER(3),    4  ord_date DATE DEFAULT NOT NULL,   5  CONSTRAINT ord_uq UNIQUE (ord_no),    6  CONSTRAINT ord_pk PRIMARY KEY (ord_no)); ord_date DATE DEFAULT NOT NULL,                       * ERROR at line 4: ORA-00936: missing expression [email protected]> CREATE TABLE ord_details   2  (ord_no NUMBER(2) ,   3  tem_no NUMBER(3),   4  ord_date DATE DEFAULT sysdate NOT NULL,   5  CONSTRAINT ord_uq UNIQUE (ord_no),   6   CONSTRAINT ord_pk PRIMARY KEY (ord_no)); CONSTRAINT ord_uq UNIQUE (ord_no),                   * ERROR at line 5: ORA-02261: such unique or primary key already exists in the table [email protected]> CREATE TABLE ord_details   2  (ord_no NUMBER(2) ,   3  tem_no NUMBER(3),   4   ord_date DATE DEFAULT sysdate NOT NULL,   5  CONSTRAINT ord_pk PRIMARY KEY (ord_no)); Table created. D答案，正確 [email protected]>  CREATE TABLE ord_details   2  (ord_no NUMBER(2),    3  item_no NUMBER(3),    4  ord_date DATE DEFAULT SYSDATE NOT NULL,   5  CONSTRAINT ord_pk PRIMARY KEY (ord_no, item_no)); Table created.