Data Types and Constraints

Choosing the right data types and enforcing constraints is fundamental to good database design. Oracle provides a rich set of data types and constraint mechanisms to ensure data integrity, performance, and storage efficiency.

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Character Data Types

Data Type	Description	Max Size
VARCHAR2(n)	Variable-length string (most common)	4,000 bytes (32,767 with MAX_STRING_SIZE=EXTENDED)
CHAR(n)	Fixed-length string (padded with spaces)	2,000 bytes
NVARCHAR2(n)	Variable-length Unicode string	4,000 bytes
NCHAR(n)	Fixed-length Unicode string	2,000 bytes
CLOB	Character Large Object	Up to 128 TB
NCLOB	Unicode Character Large Object	Up to 128 TB

Tip: Always use VARCHAR2 over CHAR unless fixed-length is specifically required. CHAR pads with trailing spaces, which can cause unexpected comparison behaviour.

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Numeric Data Types