You own a table called EMPLOYEES with this table structure: EMPLOYEE_ID NUMBER Primary Key FIRST_NAME VARCHAR2(25) LAST_NAME VARCHAR2(25) HIRE_DATE DATE What happens when you execute this DELETE statement? DELETE employees;（）
A: AYou get an error because of a primary key violation.
B: BThe data and structure of the EMPLOYEES table are deleted.
C: CThe data in the EMPLOYEES table is deleted but not the structure.
D: DYou get an error because the statement is not syntactically correct.
A: AYou get an error because of a primary key violation.
B: BThe data and structure of the EMPLOYEES table are deleted.
C: CThe data in the EMPLOYEES table is deleted but not the structure.
D: DYou get an error because the statement is not syntactically correct.
举一反三
- 下来定义表的约束语法,错误的是() A: create table t1(id number primary key,name varchar2(10)) B: create table t1(id number constraint p_k primary key(id),name varchar2(10)) C: create table t1(id number constraint p_k primary key,name varchar2(10)) D: create table t1(id number,name varchar2(10),primary key(id))
- employees表结构些如下： PLOYEE_ID NUMBER Primary Key RST_NAME VARCHAR2(25) ST_NAME VARCHAR2(25) NOT NULL 哪条语句正确插入employees一条记录？
- 下列关于主键约束的语句哪个不正确 A: CREATE TABLE STU(no INT PRIMARY KEY,name VARCHAR2(20)) B: CREATE TABLE STU(no INT,name VARCHAR2(20),PRIMARY KEY(no)) C: CREATE TABLE SCORE(sno INT,cno INT,score INT,PRIMARY KEY(sno,cno)) D: CREATE TABLE SCORE(sno INT PRIMARY KEY,cno INT PRIMARY KEY,score INT)
- SQL语句的程序清单如下： create table employees（ id char（8） primary key, name char（20） not null, department char（20） null, memo char（30） null, age int null, ） alter table employees add salary int null, drop column age, alter column memo varchar（200） null 下面说法正确的是？
- 关于以下语句，叙述正确的是 mysql > CREATE TABLE is ->( -> stuID VARCHAR(11) PRIMARY KEY, -> stuName VARCHAR(30) NOT NULL, -> stuSex VARCHAR(2) NOT NULL, -> stuBirth DATE, -> stuSchool VARCHAR(30))