Data Type Conversion from SQL Server to Oracle

Question

I am currently moving a product from SQL Server to Oracle. I am semi-familiar with SQL Server and know nothing about Oracle, so I apologize if the mere presence of this question offends anyone.

Inferring from this page, http://download.oracle.com/docs/cd/E12151_01/doc.150/e12156/ss_oracle_compared.htm, it would seem that the data type conversion from SQL Server to Oracle should be:

REAL = FLOAT(24) -> FLOAT(63)

FLOAT(p) -> FLOAT(p)

TIMESTAMP -> NUMBER

NVARCHAR(n) -> VARCHAR(n*2)

NCHAR(n) -> CHAR(n*2)

Here are my questions regarding them:

For FLOAT, considering that FLOAT(p) -> FLOAT(p), wouldn't it also mean that FLOAT -> FLOAT(24)?

For TIMESTAMP, since Oracle also has its own version of it, wouldn't it be better that TIMESTAMP -> TIMESTAMP?

Finally, for NVARCHAR(n) and NCHAR(n), I thought the issue would be regarding Unicode. Then, again, since Oracle provides its own version of both, wouldn't it make more sense that NVARCHAR(n) -> NVARCHAR(n) and NCHAR(n) -> NCHAR(n)?

It would be much appreciated if someone were to elaborate on the previous 3 matters.

Thanks in advance.

Answer 1

It appears that Oracle's CHAR and VARCHAR2 (always use VARCHAR2 instead of VARCHAR) already support Unicode - the document you've linked to advises converting to those from the SQL Server NCHAR and NVARCHAR datatypes.

The SQL Server TIMESTAMP isn't actually a timestamp at all - it's some kind of identifier based on the time that's just used to indicate that a row has changed - it can't be converted back into any kind of DATETIME (at least in a way that I know about).

For FLOAT, using 126 bytes would be enormous - since the developer tools automatically map SQL Server's FLOAT to Oracle's FLOAT(53), why not use that amount?