CHAR and VARCHAR in COBOL

In this article, we’ll explore the differences between CHAR and VARCHAR in DB2, their storage implications, performance considerations, and how VARCHAR columns map to COBOL host variables.

Understanding the CHAR Data Type in IBM DB2

The CHAR data type is used to store fixed-length character strings. When a column is defined as CHAR(n), DB2 allocates the full length n bytes for every row, regardless of the actual data stored.

Key Characteristics of CHAR

Fixed-length storage
Always padded with trailing blanks
Predictable column size
Simple internal layout

Example

CHAR(20)

If you store 'IBM', DB2 still uses 20 bytes, padding the remaining 17 bytes with spaces.

When to Use CHAR

Data with consistent length
Codes, flags, and identifiers
(e.g., COUNTRY_CODE, STATUS_FLAG)
Scenarios where fixed formatting is required

Considerations

While CHAR provides consistency, it can waste significant disk space when actual values are shorter than the defined length. This can reduce the number of rows per page and increase I/O.

Understanding the VARCHAR Data Type in DB2

The VARCHAR data type stores variable-length character data, making it more efficient when string lengths vary.

How DB2 Stores VARCHAR

DB2 typically stores:

The actual character data
A 2-byte length field indicating the number of bytes used (for columns up to 32 KB)

Key Characteristics of VARCHAR

Variable-length storage
Uses only the space required
Improves storage efficiency
Allows more rows per data page

Example

VARCHAR(100)

Storing 'test' uses:

4 bytes for data
2 bytes for length
→ Total: 6 bytes

When to Use VARCHAR

Names, descriptions, and free-text fields
Data with unpredictable or varying length
Tables where storage and I/O efficiency matter

COBOL Mapping for VARCHAR Columns

This structure is required because DB2 needs both the data and its length.

Final Thoughts

Choosing between CHAR and VARCHAR in IBM DB2 directly affects storage efficiency, performance, and application behavior—especially in COBOL‑DB2 environments. While CHAR provides simplicity and predictability, VARCHAR delivers flexibility and better space utilization.

Understanding these differences allows database designers to build scalable, efficient, and maintainable DB2 systems.

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