Nls_lang_semantics parameter importance

Question

what is the importance of nls_lang_semantics parameter.
it has two values char/bytes what is the difference between those two?
could you please clarify the exact neccesity of this parameter.

Answer 1

I assume you mean NLS_LENGTH_SEMANTICS...
By default, this is BYTE, so when you declare a column VARCHAR2(10), Oracle allocates 10 bytes of storage. Depending on your database character set, though, this may mean that the column can store between 2 and 10 characters depending on the data. In the UTF-8 character set, for example, an English character generally requires 1 byte of storage, a Japanese character generally requires 3 bytes.
Since most people want to specify things in terms of characters, NLS_LENGTH_SEMANTICS was created so that the default when you create a VARCHAR2(10) column is to allocate space for 10 characters regardless of data.
Alternalely, you can always be explicit when declaring columns, i.e. VARCHAR2(10 BYTE) and VARCHAR2(10 CHAR), but you generally want the default to be correct for your application.
Justin