以下为xs表(xh,xm,xb,bj)创建主键的命令错误的是()。
A. createtablexs(xhchar(8)primarykey,xmchar(8),xbchar(1),bjchar(20));
B. createtablexs(xhchar(8),xmchar(8),xbchar(1),bjchar(20),primarykey(xh));
C. create table xs(xh char(8),xm char(8),xb char(1),bj char(20));alter table xs add primary key(xh);
D. create table xs(xh char(8),xm char(8),xb char(1),bj char(20));alter table xs add primary key xh;
以下为xs表(xh,xm,xb,bj)创建唯一索引的命令错误的是()。
A. createtablexs(xhchar(8)primarykey,xmchar(8)unique,xbchar(1),bjchar(20));
B. createtablexs(xhchar(8)primarykey,xmchar(8),xbchar(1),bjchar(20),unique(xm));
C. create table xs(xh char(8) primary key,xm char(8),xb char(1),bj char(20));alter table xs add unique(xm);
D. create table xs(xh char(8) primary key,xm char(8),xb char(1),bj char(20));create unique index on xs(xm);
以下为xs(xh,xm,xb,bj)表bj字段创建普通索引的命令错误的是()。
A. createtablexs(xhchar(8)primarykey,xmchar(8)unique,xbchar(1),bjchar(20),index(bj));
B. createtablexs(xhchar(8)primarykey,xmchar(8)unique,xbchar(1),bjchar(20));createindexindex_bjonxs(bj);
C. create table xs(xh char(8) primary key,xm char(8) unique,xb char(1),bj char(20));alter table xs add index index_bj(bj);
D. create table xs(xh char(8) primary key,xm char(8) unique,xb char(1),bj char(20));create index on xs(bj);
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