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[,m]) |
SBCS and MBCS character data (max is 255 bytes) |
NCHAR(n) |
Same as CHAR, with specific collation
order |
NVARCHAR(n[,m]) |
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)
ORACLE
Oracle® supports the following data types to store character data:
| Oracle data type | Description |
|---|---|
CHAR(n) |
SBCS or MBCS character data using the database character set, where n is specified in bytes or characters, based on the length semantics (max is 2000 bytes) |
VARCHAR2(n) |
SBCS or MBCS character data using the database character set, where n is specified in bytes or characters, based on the length semantics (max is 4000 bytes) |
NCHAR(n) |
SBCS or MBCS character data using the national character set, where n is specified in bytes or characters, based on the length semantics (max is 2000 bytes) |
NVARCHAR2(n) |
SBCS or MBCS character data using the national character set, where n is specified in bytes or characters, based on the length semantics (max is 4000 bytes) |
MAX_STRING_SIZE=EXTENDED server parameter. Use
VARCHAR2 type can get a size up to 32Kb when
MAX_STRING_SIZE=EXTENDED is set. However, the storage technique used by Oracle 12c for such a large string type is
different from the native/standard VARCHAR2(4000) type. Large character strings
will be stored as LOBs. Extended character types are not supported by Genero's Oracle database driver.In Oracle
CHAR(N)/VARCHAR2(N) types, the size N can be specified in character or byte units,
depending on length semantics settings. See Length semantics settings for more
details.
When comparing CHAR and VARCHAR2 values in Oracle, the trailing
blanks are significant; this is not the case when using Informix
VARCHAR columns. However, before comparing string values, Oracle blank-pads CHAR(N) data to the maximum
length of both operands. As result, it looks like trailing blanks are not significant in
CHAR(N) comparison. For example, a column defined as CHAR(5) with
the value 'abc ' (with 2 trailing blanks) will not be equal to
'abc', but when comparing (col = 'abc'), Oracle will add 2 blanks to the right operand and values will
match. Blank padding does not occur for VARCHAR2() data, as result, the expression
(col = 'abc') will be false, if col VARCHAR2 does not exactly
contain the value 'abc'. For more details, see blank-padded and non-padded
comparison semantics in Oracle
documentation.
Oracle treats empty strings like
NULL values; Informix doesn't. See issue
Empty Character Strings for more
details.
With Oracle, you can define a Database Character Set and a National Character Set.Oracle uses the Database Character Set to
store string data in the CHAR/VARCHAR2 columns, and uses the National Character Set
for NCHAR/NVARCHAR2 columns.
Solution
Informix
CHAR(N) types must be mapped to Oracle
CHAR(N) types, and Informix
VARCHAR(N) or LVARCHAR(N) columns must be mapped to Oracle
VARCHAR2(N).
Check that your database tables do not use CHAR, VARCHAR or
LVARCHAR types with a length exceeding the Oracle limits of CHAR/VARCHAR2.
When using a multibyte character set (such as UTF-8), configure Oracle to use character length semantics, define
CHAR/VARCHAR2 database columns with a size in character units, and use character
length semantics in BDL programs with FGL_LENGTH_SEMANTICS=CHAR. See Length semantics settings for more details.
When extracting a database schema from an Oracle database, the fgldbsch
schema extractor uses the size of the column in characters, not the octet length. If you have
created a CHAR(10 (characters) ) column a in the database, the
.sch file will get a size of 10, that will be interpreted according to
FGL_LENGTH_SEMANTICS as a number of bytes or characters.
The Oracle client character set must correspond to the Genero runtime system locale (LANG/LC_ALL). You can define the Oracle client character set with the NLS_LANG environment variable.
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 }