CHAR and VARCHAR data types
Informix®
Informix supports the following character data types:
| Informix data type | Description |
|---|---|
CHAR(n) |
SBCS and MBCS character data (max is 32767 bytes) |
VARCHAR(n |
SBCS and MBCS character data (max is 255 bytes) |
NCHAR(n) |
Same as CHAR, with specific collation
order |
NVARCHAR(n |
Same as VARCHAR, with specific collation
order |
LVARCHAR(n) |
max size varies depending on the IDS version |
With Informix, both
CHAR/VARCHAR and NCHAR/NVARCHAR data types can be used to store
single-byte or multibyte encoded character strings. The only difference between
CHAR/VARCHAR and NCHAR/NVARCHAR is in how they use sorting:
N[VAR]CHAR types use the collation order, while [VAR]CHAR types
use the byte order.
The character set used to store strings in
CHAR/VARCHAR/NCHAR/NVARCHAR columns is defined by the DB_LOCALE environment
variable.
Informix uses Byte Length Semantics (the size
N that you specify in [VAR]CHAR(N) is expressed in bytes, not characters as in some
other databases)
IBM® DB2®
IBM DB2 supports following data types to store character data:
| IBM DB2 data type | Description |
|---|---|
CHAR(n) |
SBCS or MBCS character data using the database character set,
where n is specified in bytes, or characters when the string
units is CODEUNITS32. (max is 255 bytes) |
VARCHAR(n) |
SBCS or MBCS character data using the database character set,
where n is specified in bytes, or characters when the string
units is CODEUNITS32. (max is 32672 bytes) |
GRAPHIC(n) |
UNICODE character data, where
n is specified in double-bytes, or characters when the string units is
CODEUNITS32 (max is 127 characters) |
VARGRAPHIC(n) |
UNICODE character data, where
n is specified in double-bytes, or characters when the string units is
CODEUNITS32 .
(max is 16336 characters) |
NCHAR(n) |
Synonym for CHAR or GRAPHIC,
depending on the nchar_mapping database parameter, where
n is specified in characters. |
NVARCHAR(n) |
Synonym for VARCHAR or
VARGRAPHIC, depending on the nchar_mapping database parameter, where
n is specified in characters. |
The character set used by DB2 to store
CHAR and VARCHAR data is defined in the database locale section
when creating a new database. If your application uses UTF-8, consider creating the DB2 database with the UTF-8 codeset.
The DB2
NLS_STRING_UNITS=CODEUNITS32 built-in global variable
(string_units system variable) can be used to control the real size in bytes of
character data types. See DB2 documentation for more details.
- On Linux and UNIX operating systems, the default code page determined from the locale setting, which includes information about language, territory and code set.
- On Windows operating systems, the default code page is derived from the ANSI code page setting in the Regional Options menu in the Control Panel.
Solution
Informix CHAR(N) columns can be
converted to DB2 CHAR(N) or
NCHAR(N) types, and Informix
VARCHAR(N) or LVARCHAR(N) columns can be converted to DB2 VARCHAR(N) or
NVARCHAR(N).
Table columns using a different character encoding than the database is not supported with Genero: All table columns must use the same character encoding defined at the database level.
Based on the FGLPROFILE entry dbi.database.dbname.ifxemul.nationalchars, the
CHAR and VARCHAR type names in SQL statements are converted to
CHAR/VARCHAR or to NCHAR/NVARCHAR DB2 types, that are then
interpreted by DB2 to CHAR/VARCHAR or GRAPGHIC/VARGRAPHIC types,
depending on the nchar_mapping database parameter.
Check that your database schema does not use CHAR or VARCHAR
types with a length exceeding the DB2 limits. Especially, the
Informix CHAR type has a very long size
limit compared to DB2 CHAR. For example,
when using the ifxemul.nationalchars FGLPROFILE entry, if a program creates a table
with a CHAR(100) column, the ODI driver will convert this to
NCHAR(100), and if nchar_mapping=CHAR_CU32, DB2 will convert
NCHAR(100) to a CHAR(100) with CODEUNITS32, which will result in a
CHAR(400) (100*4), which exceeds the maximum size (255 bytes) of a
DB2 CHAR.
When using a multibyte character set (such as UTF-8) in programs, if the DB2 database was created with the appropriate codeset (UTF-8), use
the CHAR/VARCHAR column types, and use BYTE length semantics in programs. Another
option is to use CHAR/VARCHAR types, with the
NLS_STRING_UNITS=CODEUNITS32 option set, to force DB2 to apply a ratio of 4 for
storage sizes, and use CHAR length semantics in programs. If the DB2 database codeset is not
multibyte, you must use the GRAPHIC and VARGRAPHIC data types to
store multibyte character data, and use CHAR length semantics in programs.
When generating a .sch database schema from a DB2 database, the fgldbsch schema extractor extracts the size of
CHAR/VARCHAR columns and GRAPHIC/VARGRAPHIC columns as a number of
characters. If you have created a CHAR(10) column a in DB2 database using the UTF-8 character set, the .sch file
will get a size of 10, that will be interpreted by FGL_LENGTH_SEMANTICS as either a number of bytes
or characters.
On Linux and UNIX operating systems,
DB2CODEPAGE can be left unset, since DB2 client will use the current application locale as default.
On Microsoft Windows platforms, if the ANSI Code Page of the operating system does not match the
LANG setting used by Genero applications (LANG=.fglutf8), the DB2CODEPAGE must be
set. For UTF-8, DB2CODEPAGE=1208; for ISO-8859-15, DB2CODEPAGE=923.
See also the section about Localization.
CHAR/VARCHAR type translation can be controlled with the following FGLPROFILE
entries:dbi.database.dsname.ifxemul.datatype.char = { true | false }
dbi.database.dsname.ifxemul.datatype.varchar = { true | false }