- Prior to Oracle Database 12c the maximum length for a VARCHAR2 and NVARCHAR2 was 4,000, and the maximum length of a RAW column was 2,000. Starting with Oracle Database 12c, these data types have been extended to accommodate a length of 32,767.
- Prior to Oracle Database 12c, you could not have multiple indexes defined on the exact same combination of columns in one table. This has changed in 12c. You can now have multiple indexes on the same set of columns. However, you can only do this if there is something physically different about the indexes; for example, one index is created as a B-tree index, and the second, as a bitmap index. Also, there can be only one visible index for the same combination of columns. Any other indexes created on that same set of columns must be declared invisible;
- The NVARCHAR2 and NCHAR data types are useful if you have a database that was originally created with a single-byte,
- If you use a VARCHAR2 for a field that contains date information, you are guaranteeing future reporting inconsistencies and needless conversion function(such as TO_DATE and TO_CHAR). fixed-width character set, but sometime later you need to store multibyte character set data in the same database.
- The RAW data type allows you to store binary data in a column. This type of data is sometimes used for storing globallyunique identifiers or small amounts of encrypted data. If you need to store large amounts (over 2000 bytes) of binary data then use a BLOB instead.
- You can also instruct Oracle to not re-adjust the high-water mark when shrinking a table. This is done via theCOMPACT clause—for example:
- SQL> alter table emp shrink space compact;