NCHAR in Oracle 9i

Question

Hi,
I'm using Oracle 9i and implementing internationalization for my application. On the oracle site, it says that Oracle 9i supports NCHAR which is an unicode datatype exclusively. But i found that VARCHAR2 also stores unicode characters perfectly.
Q: So why do we use NCHAR datatypes?
It also says that we do not need to change the Database Character Set. We just need to make the National Character Set equal to UTF8 or AL16UTF16 and add the column NCHAR datatype to store unicode in a non-unicode database.
But i tried this :
Database Character Set: WE8MSWIN1252
National Character Set: AL16UTF16 (default)
and i still cant store my unicode.
Please advise. Thanks

Answer 1

Perhaps this information is going to clear in better
way your question:
NCHAR
You use the NCHAR datatype to store fixed-length (blank-padded if necessary) national character data. How the data is represented internally depends on the national character set specified when the database was created, which might use a variable-width encoding (UTF8) or a fixed-width encoding (AL16UTF16). Because this type can always accommodate multibyte characters, you can use it to hold any Unicode character data.
The NCHAR datatype takes an optional parameter that lets you specify a maximum size in characters. The syntax follows:
NCHAR[(maximum_size)]
Because the physical limit is 32767 bytes, the maximum value you can specify for the length is 32767/2 in the AL16UTF16 encoding, and 32767/3 in the UTF8 encoding.
You cannot use a symbolic constant or variable to specify the maximum size; you must use an integer literal.
If you do not specify a maximum size, it defaults to 1. The value always represents the number of characters, unlike CHAR which can be specified in either characters or bytes.
my_string NCHAR(100); -- maximum size is 100 characters
The maximum width of an NCHAR database column is 2000 bytes. So, you cannot insert NCHAR values longer than 2000 bytes into an NCHAR column.
If the NCHAR value is shorter than the defined width of the NCHAR column, Oracle blank-pads the value to the defined width.
You can interchange CHAR and NCHAR values in statements and expressions. It is always safe to turn a CHAR value into an NCHAR value, but turning an NCHAR value into a CHAR value might cause data loss if the character set for the CHAR value cannot represent all the characters in the NCHAR value. Such data loss can result in characters that usually look like question marks (?).
NVARCHAR2
You use the NVARCHAR2 datatype to store variable-length Unicode character data. How the data is represented internally depends on the national character set specified when the database was created, which might use a variable-width encoding (UTF8) or a fixed-width encoding (AL16UTF16). Because this type can always accommodate multibyte characters, you can use it to hold any Unicode character data.
The NVARCHAR2 datatype takes a required parameter that specifies a maximum size in characters. The syntax follows:
NVARCHAR2(maximum_size)
Because the physical limit is 32767 bytes, the maximum value you can specify for the length is 32767/2 in the AL16UTF16 encoding, and 32767/3 in the UTF8 encoding.
You cannot use a symbolic constant or variable to specify the maximum size; you must use an integer literal.
The maximum size always represents the number of characters, unlike VARCHAR2 which can be specified in either characters or bytes.
my_string NVARCHAR2(200); -- maximum size is 200 characters
The maximum width of a NVARCHAR2 database column is 4000 bytes. Therefore, you cannot insert NVARCHAR2 values longer than 4000 bytes into a NVARCHAR2 column.
You can interchange VARCHAR2 and NVARCHAR2 values in statements and expressions. It is always safe to turn a VARCHAR2 value into an NVARCHAR2 value, but turning an NVARCHAR2 value into a VARCHAR2 value might cause data loss if the character set for the VARCHAR2 value cannot represent all the characters in the NVARCHAR2 value. Such data loss can result in characters that usually look like question marks (?).
Joel P�rez