数据库系统基础教程答案ch4 4.1.1
4.1.2
a)
cargo是什么意思
b)
c)
In c we assume that a phone and address can only belong to a single customer (1-m relationship reprented by arrow into customer).
vram
d)
In d we assume that an address can only belong to one customer and a phone can
exist at only one address.
If the multiplicity of above relationships were m-to-n, the entity t becomes
weak and the key ssNo of customers will be needed as part of the composite key
of the entity t.
In c&d, we convert attributes phones and address to entity ts. Since entity
ts often become relations in relational design,
we must consider more efficient alternatives.
暑假小学英语培训Instead of querying multiple tables where key values are duplicated, we can also modify attributes:李娜 英文
(i) Phones attribute can be converted into HomePhone, OfficePhone and CellPhone. (ii) A multivalued attribute such as alias can be kept as an attribute where a
lanusingle column can be ud in relational concatenate all values. SQL
allows a query "like '%Junius%'" to arch the multiple values in a column alias.经典英文句子
4.1.3
4.1.4asiantube8
音乐的英文单词
a)
b)
okaya英语口语班成都c)
The relationship "played" between Teams and Players is similar to relationship "plays" between Teams and Players.
4.1.5
