About InterBase Data Types

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When creating a new column in an InterBase table, the primary attribute that you must define is the data type, which establishes the set of valid data that the column can contain. Only values that can be represented by that data type are allowed. Besides establishing the set of valid data that a column can contain, the data type defines the kinds of operations that you can perform on the data. For example, numbers in INTEGER columns can be manipulated with arithmetic operations, while CHARACTER columns cannot.

The data type also defines how much space each data item occupies on the disk. Choosing an optimum size for the data value is an important consideration when disk space is limited, especially if a table is very large. InterBase supports the following data types:

INTEGER and SMALLINT
FLOAT and DOUBLE PRECISION
NUMERIC and DECIMAL
DATE, TIME,andTIMESTAMP
CHARACTER and VARYING CHARACTER
BOOLEAN
BLOB

InterBase provides the Blob data type to store data that cannot easily be stored in one of the standard SQL data types. A BLOB is used to store data objects of indeterminate and variable size, such as bit-mapped graphics images, vector drawings, sound files, video segments, chapter or book-length documents, or any other kind of multimedia information. InterBase also supports arrays of most data types. An array is a matrix of individual items composed of any single InterBase data type (except BLOB). An array can have from 1 to 16 dimensions. An array can be handled as a single entity, or manipulated item-by-item.

A TIMESTAMP data type is supported that includes information about year, month, day of the month, and time. The TIMESTAMP data type is stored as two long integers, and requires conversion to and from InterBase when entered or manipulated in a host-language program. The DATE data type includes information on the year, month, and day of the month. The TIME data type includes information about time in hours, minutes, seconds, and tenths, hundredths, and thousandths of seconds.

The following table describes the data types supported by InterBase:

Name	Size	Range/Precision	Description
`BLOB`	Variable	None Blob segment size is limited to 64K	Dynamically sizable data type for storing large data such as graphics, text, and digitized voice Basic structural unit is the segment Blob subtype describes Blob contents
BOOLEAN	16 bits	`TRUE` `FALSE` `UNKNOWN`	Represents truth values `TRUE`, `FALSE`, and `UNKNOWN` Requires ODS 11 or higher, any dialect
`CHAR`(<n>)	<n> characters	1 to 32,767 bytes Character set character size determines the maximum number of characters that can fit in 32K	Fixed length `CHAR` or text string type Alternate keyword: `CHARACTER`
`DATE`	32 bits	1 Jan 100 a.d. to 29 Feb 32768 a.d.	Stores a date as a 32-bit longword
`DECIMAL` (<precision>, <scale>)	Variable (16, 32, or 64 bits)	<precision> = 1 to 18; specifies at least <precision> digits of precision to store <scale> = 0 to 18; specifies number of decimal places must be less than or equal to <precision>	Number with a decimal point <scale> digits from the right Example: `DECIMAL`(10,3) holds numbers accurately in the following format: ppppppp.sss
`DOUBLE PRECISION`	64 bits¹	2.225 x 10^–308to 1.797 x 10³⁰⁸	IEEE double precision: 15 digits
`FLOAT`	32 bits	1.175 x 10^–38 to 3.402 x 10³⁸	IEEE single precision: 7 digits
`INTEGER`	32 bits	–2,147,483,648 to 2,147,483,647	Signed long (longword)
`NUMERIC` (<precision>, <scale>)	Variable (16, 32, or 64 bits)	<precision> = 1 to 18; specifies exactly <precision> digits of precision to store <scale> = 0 to 18; specifies number of decimal places and must be less than or equal to <precision>	Number with a decimal point <scale> digits from the right Example: `NUMERIC`(10,3) holds numbers accurately in the following format: ppppppp.sss
`SMALLINT`	16 bits	–32,768 to 32,767	Signed short (word)
TIME	32 bits	0:00 AM-23:59:59.9999 PM	Unsigned integer of InterBase type `ISC_TIME`: time of day, in units of 0.0001 seconds since midnight
TIMESTAMP	64 bits	1 Jan 100 a.d. to 29 Feb 32768 a.d.	InterBase type `ISC_TIMESTAMP`; combines `DATE` and `TIME` information
`VARCHAR` (<n>)	<n> characters	1 to 32,765 bytes Character set character size determines the maximum number of characters that can fit in 32K	Variable length `CHAR` or text string type Alternate keywords: `CHAR VARYING`, `CHARACTER VARYING`

Actual size of DOUBLE is platform-dependent. Most platforms support the 64-bit size.

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