Data Type

Oracles supports the following categories of data types:
Oracle Built-in Datatypes.
User-Defined Data Types.

There are 20 Oracle built-in data types, divided into 6 groups:
1.Character Datatypes - CHAR, NCHAR, NVARCHAR2, VARCHAR2
2.Number Datatypes - NUMBER, BINARY_FLOAT, BINARY_DOUBLE
3.Long and Row Datatypes - LONG, LONG RAW, RAW
4.Datetime Datatypes - DATE, TIMESTAMP, INTERVAL YEAR TO MONTH, INTERVAL DAY TO SECOND
5.Large Object Datatypes - BLOB, CLOB, NCLOB, BFILE
6.Row ID Datatypes - ROWID, UROWID

Difference between  CHAR and NCHAR:
Both CHAR and NCHAR are fixed length character data types. But they have the following differences:
CHAR's size is specified in bytes by default.
NCHAR's size is specified in characters by default. A character could be 1 byte to 4 bytes long depending on the character set used.
NCHAR stores characters in Unicode.

Difference between  CHAR and VARCHAR2 :
The main differences between CHAR and VARCHAR2 are
CHAR stores values in fixed lengths. Values are padded with space characters to match the specified length.
VARCHAR2 stores values in variable lengths. Values are not padded with any characters.

Difference between  NUMBER and BINARY_FLOAT :
The main differences between NUMBER and BINARY_FLOAT are
NUMBER stores values as fixed-point numbers using 1 to 22 bytes.
BINARY_FLOAT stores values as single precision floating-point numbers.

Difference between  DATE and TIMESTAMP :
The main differences between DATE and TIMESTAMP are
DATE stores values as century, year, month, date, hour, minute, and second.
TIMESTAMP stores values as year, month, day, hour, minute, second, and fractional seconds.

Difference between  INTERVAL YEAR TO MONTH and INTERVAL DAY TO SECOND:
The main differences between INTERVAL YEAR TO MONTH and INTERVAL DAY TO SECOND are:
INTERVAL YEAR TO MONTH stores values as time intervals at the month level.
INTERVAL DAY TO SECOND stores values as time intervals at the fractional seconds level.

Difference between  BLOB and CLOB :
The main differences between BLOB and CLOB are:
BLOB stores values as LOB (Large OBject) in bitstreams.
CLOB stores values as LOB (Large OBject) in character steams.