Re: question about CAST and Multiset# Database - 数据库
s*c
1 楼
Hi,composite:
As for user defined data type support of Cast, I think it
depends on the specified DBMS.
"Multiset" is unrelated with "Cast". It's not a function,
but a concept. It is the definition of multiset: An
unordered collection of objects that are not necessarily
distinct. The collection may be empty.
Because SQL allows duplicate rows in a table, or applied
aggregate funcitons may result in duplicate rows, by
default,
SQL treats a table generated by select or group by as a
mutliset rather
As for user defined data type support of Cast, I think it
depends on the specified DBMS.
"Multiset" is unrelated with "Cast". It's not a function,
but a concept. It is the definition of multiset: An
unordered collection of objects that are not necessarily
distinct. The collection may be empty.
Because SQL allows duplicate rows in a table, or applied
aggregate funcitons may result in duplicate rows, by
default,
SQL treats a table generated by select or group by as a
mutliset rather