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例如下面的建表语句:
CREATE TABLE PERSON
(NAME CHAR (16) NOT NULL,
ID CHAR (09) NOT NULL,
AGE NUMBER (9) DEFAULT (0),
BIRTH CHAR (0 NOT NULL,
CONSTRAINT PERSONPK
PRIMARY KEY (NAME,
ID),
CONSTRAINT PERSONUK_01
UNIQUE (NAME,
BIRTH DESC,
ID),
CONSTRAINT PERSONUK_02
UNIQUE (NAME,
BIRTH,
ID DESC);
这两个PERSONUK_01和PERSONUK_02是干什么用的?
DESC作什么用?是新建数据的时候按照BIRTH和ID的降序插入吗?如果是的话,怎么可能既按照BIRTH的降序插入,又按照ID的降序插入?
有相应的ASC吗?
下面这样写允许吗?
例如下面的建表语句:
CREATE TABLE PERSON1
(NAME CHAR (16) NOT NULL,
ID CHAR (09) NOT NULL,
AGE NUMBER (9) DEFAULT (0),
BIRTH CHAR (0 NOT NULL,
CONSTRAINT PERSONPK
PRIMARY KEY (NAME,
ID),
CONSTRAINT PERSONUK_01
UNIQUE (NAME,
BIRTH DESC,
ID),
CONSTRAINT PERSONUK_02
UNIQUE (NAME,
BIRTH ASC,
ID ); |
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