Oracle data type choice: For an alphanumeric field with variable length, which data type is best to store values efficiently while avoiding unnecessary padding?

Introduction / Context:
Correct data types ensure storage efficiency and predictable behavior. In Oracle, character columns can be fixed length or variable length; picking the right one avoids wasted space and subtle comparison issues.

Given Data / Assumptions:

• Field is alphanumeric (textual) and varies in length by row.
• Values should not be padded to a fixed width.
• Standard Oracle data types are available.

Concept / Approach:

Use VARCHAR2 for variable-length character data. Oracle stores only the bytes required for the value plus small overhead. CHAR is fixed-length and space-pads values to the declared size, which wastes space and can affect comparisons. LONG is legacy (large unstructured text) and discouraged in favor of CLOB. NUMBER is numeric and not appropriate for alphanumeric text.

Step-by-Step Solution:

Verification / Alternative check:

Compare storage and behavior: inserting 'A' into CHAR(10) pads to 10, whereas VARCHAR2(10) stores 1 character.

Why Other Options Are Wrong:

CHAR: fixed length; wasteful for varying sizes.

LONG: obsolete; limited functions and should be replaced by CLOB.

NUMBER: numeric type; cannot store general text.

Common Pitfalls:

Declaring CHAR for codes that actually vary, leading to trailing-space anomalies in joins and comparisons.

Final Answer:

VARCHAR2