Numeric data types


Informix supports several data types to store numbers:

Table 1. Informix numeric data types
Informix data type Description
SMALLINT 16 bit signed integer
INTEGER 32 bit signed integer
BIGINT 64 bit signed integer
INT8 64 bit signed integer (replaced by BIGINT)
DECIMAL Equivalent to DECIMAL(16)
DECIMAL(p) Floating-point decimal number (max precision is 32)
DECIMAL(p,s) Fixed-point decimal number (max precision is 32)
MONEY Equivalent to DECIMAL(16,2)
MONEY(p) Equivalent to DECIMAL(p,2) (max precision is 32)
MONEY(p,s) Equivalent to DECIMAL(p,s) (max precision is 32)
REAL / SMALLFLOAT 32-bit floating point decimal (C float)
DOUBLE PRECISION / FLOAT[(n)] 64-bit floating point decimal (C double)


Oracle® supports following data types to store numbers:

Table 2. Oracle numeric data types
Oracle data type Description
NUMBER(p,s) (1<=p<= 38, -84<=s<=127) Fixed point decimal numbers.
NUMBER(p) (1<=p<= 38) Integer numbers with a precision of p digits.
NUMBER(*,s) Fixed point decimal numbers with a precision of 38 digits.
NUMBER Floating point decimals with a precision of 38 digits.
FLOAT(b) (1<=b<= 126) Floating point numbers with a binary precision b. This is a sub-type of NUMBER.
BINARY_FLOAT 32-bit floating point number.
BINARY_DOUBLE 64-bit floating point number.

The type names SMALLINT, INTEGER are supported by Oracle. However, these will be converted to the native NUMBER(*,0) type. When dividing INTEGER or SMALLINT types, Informix rounds the result ( 7 / 2 = 3 ), while Oracle doesn't, because it does not have a native integer data type ( 7 / 2 = 3.5 )

The DECIMAL type name is also supported by Oracle, and is mapped to the native NUMBER type. When using a precision and scale (DECIMAL(p,s)), the resulting NUMBER(p,s) type is equivalent. However, DECIMAL(p) becomes a NUMBER(p,0), and DECIMAL without precision / scale becomes a NUMBER(*,0) both storing whole numbers. This is different from Informix SQL, where a DECIMAL (with or without precision) can store real numbers.
Oracle NUMBER without precision / scale can store real numbers, while Oracle DECIMAL will store whole numbers. For example:
INSERT INTO t1 VALUES ( 123.456, 123.456 );
       NUM	  DEC
---------- ----------
   123.456	  123


Use the following conversion rules to map Informix numeric types to Oracle numeric types:

Table 3. Informix numeric types and Oracle equivalents
Informix data type Oracle data type
DECIMAL(p) FLOAT(p * 3.32193)
DECIMAL (not recommended) FLOAT
MONEY(p,s) NUMBER(p,s)

Avoid dividing integers in SQL statements. If you do divide an integer, use the TRUNC() function with Oracle.

When creating a table directly in Oracle's sqlplus with the INTEGER, SMALLINT types, Oracle will create columns with the native NUMBER(38,0) type. As result, it is not possible (for fgldbsch) to distinguish the original type names used in CREATE TABLE from the native NUMBER(38,0) type or NUMBER(38) type (where scale defaults to zero). In the next example, all columns will be of type NUMBER(38,0):
$ sqlplus ...
sql> CREATE TABLE mytab (
   col1 INTEGER,
   col2 SMALLINT,
   col3 NUMBER(38),
When extracting the database schema with fgldbsch, NUMBER, NUMBER(p>32) and NUMBER(p>32,s) types will by default give an extraction error. However, these types can be converted to DECIMAL(32) and DECIMAL(32,s) with the -cv option, by using the "B" character at positions 22 (for NUMBER) and 23 (for NUMBER(p>32[,s])).

When fetching a NUMBER[(p>32,s)] into a BDL DECIMAL(32[,s]) type, if the value stored in the NUMBER column has more than 32 digits, it will be rounded to fit into a DECIMAL(32), or the overflow error -1226 will occur when fetching into a DECIMAL(32,s). Note that it must be allowed to fetch numeric expressions such as 1/3 (=0.333333333333....) into a DECIMAL(p,s), even if such expression will produce more than 32 digits with Oracle.

When creating a table in a BDL program with DECIMAL(p), this type is converted to native Oracle FLOAT(p*3.32193). When creating a table in a BDL program with DECIMAL (without precision) this type is converted to native Oracle FLOAT. The native Oracle FLOAT[(p)] type can be extracted by fgldbsch, but Oracle's FLOAT has a higher precision than the BDL DECIMAL type, which can lead to value rounding when fetching rows.

When casting a numeric expression such as CAST(SUM(col) AS DECIMAL), with Informix SQL this results in a real numeric value. With Oracle the DECIMAL type becomes a NUMBER(*,0) and the result is a whole number. The DECIMAL type name in the CAST() expression is not translated by the Oracle drivers because this type conversion is only done for DDL statement (CREATE TABLE / ALTER TABLE).


As a general recommendation, do not use DECIMAL[(p)] or SMALLFLOAT/FLOAT floating point types in business applications. These types should only be used for scientific data storage.

The numeric types translation can be controlled with the following FGLPROFILE entries:
dbi.database.dsname.ifxemul.datatype.smallint = { true | false }
dbi.database.dsname.ifxemul.datatype.integer = { true | false }
dbi.database.dsname.ifxemul.datatype.bigint = { true | false }
dbi.database.dsname.ifxemul.datatype.int8 = { true | false }
dbi.database.dsname.ifxemul.datatype.decimal = { true | false } = { true | false }
dbi.database.dsname.ifxemul.datatype.float = { true | false }
dbi.database.dsname.ifxemul.datatype.smallfloat = { true | false }
For more details see IBM Informix emulation parameters in FGLPROFILE.