Data Encoding

This page covers how DB2 encodes data on the wire: the FD:OCA format, type system, CCSID negotiation, and EBCDIC handling.

TYPDEFNAM (Type Definition Name)

During ACCRDB, the client and server negotiate a Type Definition Name that controls data encoding. Common values:

Name	Description
QTDSQLX86	Intel x86 — little-endian integers, IEEE float, UTF-8
QTDSQLASC	ASCII-based systems
QTDSQLBC	Big-endian systems (z/OS)

db2-node always requests QTDSQLX86 to ensure standard encoding.

TYPDEFOVR (Type Definition Overrides)

Override the CCSID (Coded Character Set Identifier) to request UTF-8 encoding:

Parameter	CCSID	Encoding
CCSIDSBC (single-byte)	1208	UTF-8
CCSIDDBC (double-byte)	1200	UTF-16
CCSIDMBC (mixed-byte)	1208	UTF-8

By negotiating CCSID 1208, all string data is exchanged in UTF-8, avoiding EBCDIC conversion.

Row Data Format (QRYDTA)

Rows in QRYDTA are encoded as:

[Null indicator(s)] [Column 1 data] [Column 2 data] ...

Null Indicators

Each nullable column has a 1-byte null indicator: - 0xFF = NULL - 0x00 = not null (data follows)

Column Data Encoding

DB2 Type	Wire Format
SMALLINT	2 bytes, big-endian signed i16
INTEGER	4 bytes, big-endian signed i32
BIGINT	8 bytes, big-endian signed i64
REAL	4 bytes, IEEE 754 float
DOUBLE	8 bytes, IEEE 754 double
DECIMAL	Packed BCD (Binary Coded Decimal)
CHAR(n)	Fixed n bytes, space-padded
VARCHAR(n)	2-byte length prefix (BE) + UTF-8 bytes
DATE	10 bytes: YYYY-MM-DD
TIME	8 bytes: HH.MM.SS
TIMESTAMP	26 bytes: YYYY-MM-DD-HH.MM.SS.ffffff
BOOLEAN	1 byte: 0x00 = false, 0x01 = true

Packed BCD (Decimal)

DECIMAL values use Packed Binary Coded Decimal encoding: - Each byte holds two decimal digits (4 bits each) - The last nibble is the sign: 0xC = positive, 0xD = negative, 0xF = unsigned - Example: 12345 with precision 5 = 0x01 0x23 0x45 0x0C

FD:OCA (Formatted Data Object Content Architecture)

FD:OCA defines the structure of result set data. The QRYDSC (Query Description) contains FD:OCA triplets that describe:

1. Data type — The DRDA type code for each column
2. Length — Fixed or variable length
3. Nullability — Whether the column can be null
4. CCSID — Character set for string columns

FD:OCA Triplet Format

[Type byte] [Length] [Data...]

The triplet types define how to interpret the column data in QRYDTA.

EBCDIC Handling

DB2 on z/OS and AS/400 uses EBCDIC encoding. DB2 on Linux/Windows uses ASCII/UTF-8.

Strategy

1. Always negotiate UTF-8 (CCSID 1208) during connection via TYPDEFOVR
2. Maintain a minimal EBCDIC 037 conversion table as fallback
3. The RDBNAM (database name) in ACCSEC/ACCRDB may require EBCDIC encoding on older servers

EBCDIC Code Page 037

Code Page 037 is the US/Canada EBCDIC variant. Key mappings:

ASCII	EBCDIC 037
A	0xC1
Z	0xE9
0	0xF0
9	0xF9
Space	0x40

db2-node includes a complete 256-byte bidirectional lookup table for EBCDIC 037 conversion.

DB2 SQL Type Codes

DRDA Code	DB2 Type
0x05	SMALLINT
0x03	INTEGER
0x17	BIGINT
0x07	REAL
0x0F	DOUBLE
0x0B	DECIMAL
0x21	DATE
0x23	TIME
0x25	TIMESTAMP