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question# Database - 数据库

C*e2000-06-21 07:06

1 楼

I have a question here:
What do CAST and MULTISET do in SQL language?
I read in a book that CAST converts a specified scalar value to
a specified scalar data type (maybe a user defined data type),
is that true? Does it take at least two arguments (value and the
data type)?
And I can't find MULTISET. Please give me a hand.
Thanks.

s*c2000-06-21 07:06

2 楼

CAST is a reversed word in SQL2 Standard. Generaly, it
should have two
argus: value and new data type. But in diffrent DBMSs, the
syntax maybe a little diffrent, so you'd better refer to
your server's documents. Convert is another funtion similar
with Cast.
For SQL Server, the syntax is: CAST(expression as datatype),
and it doesn't suporrt user-defined datatype in CAST.

【在 C*******e 的大作中提到】

: I have a question here:
: What do CAST and MULTISET do in SQL language?
: I read in a book that CAST converts a specified scalar value to
: a specified scalar data type (maybe a user defined data type),
: is that true? Does it take at least two arguments (value and the
: data type)?
: And I can't find MULTISET. Please give me a hand.
: Thanks.

C*e2000-06-21 07:06

3 楼

Thanks!
Since I was looking at relational/object DBMS, CAST
now is extended to user defined data type also, I guess,
in SQL extensions. And probabely MULTISET serves similar
function together with CAST, but I really couldn't find
this guy.

【在 s*****c 的大作中提到】

:
: CAST is a reversed word in SQL2 Standard. Generaly, it
: should have two
: argus: value and new data type. But in diffrent DBMSs, the
: syntax maybe a little diffrent, so you'd better refer to
: your server's documents. Convert is another funtion similar
: with Cast.
: For SQL Server, the syntax is: CAST(expression as datatype),
: and it doesn't suporrt user-defined datatype in CAST.