The optional SUB_TYPE parameter specifies the nature of data written to the column. Firebird provides two pre-defined subtypes for storing user data:

Subtype 0: BINARY

If a subtype is not specified, the specification is assumed to be for untyped data and the default SUB_TYPE 0 is applied. The alias for subtype zero is BINARY. This is the subtype to specify when the data are any form of binary file or stream: images, audio, word-processor files, PDFs and so on.

Subtype 1: TEXT

Subtype 1 has an alias, TEXT, which can be used in declarations and definitions. For instance, BLOB SUB_TYPE TEXT. It is a specialized subtype used to store plain text data that is too large to fit into a string type. A CHARACTER SET may be specified, if the field is to store text with a different encoding to that specified for the database. From Firebird 2.0, a COLLATE clause is also supported.

Specifying a CHARACTER SET without SUB_TYPE implies SUB_TYPE TEXT.

Custom SubtypesIt is also possible to add custom data subtypes, for which the range of enumeration from -1 to -32,768 is reserved. Custom subtypes enumerated with positive numbers are not allowed, as the Firebird engine uses the numbers from 2-upward for some internal subtypes in metadata.

SizeThe maximum size of a BLOB field is limited to 4GB, regardless of whether the server is 32-bit or 64-bit. (The internal structures related to BLOBs maintain their own 4-byte counters.) For a page size of 4 KB (4096 bytes) the maximum size is lower — slightly less than 2GB.

Operations and ExpressionsText BLOBs of any length and any character set — including multi-byte — can be operands for practically any statement or internal functions. The following operators are supported completely:

Partial support:

• An error occurs with these if the search argument is larger than or equal to 32 KB:

  STARTING [WITH],	LIKE,
  CONTAINING

• Aggregation clauses work not on the contents of the field itself, but on the BLOB ID. Aside from that, there are some quirks:

  SELECT DISTINCT	returns several NULL values by mistake if they are present
  ORDER BY	—
  GROUP BY	concatenates the same strings if they are adjacent to each other, but does not do it if they are remote from each other

See alsoFILTER, DECLARE FILTER

The support of arrays in the Firebird DBMS is a departure from the traditional relational model. Supporting arrays in the DBMS could make it easier to solve some data-processing tasks involving large sets of similar data.

Arrays in Firebird are stored in BLOB of a specialized type. Arrays can be one-dimensional and multidimensional and of any data type except BLOB and ARRAY.

Example

  |CREATE TABLE SAMPLE_ARR (
  |  ID INTEGER NOT NULL PRIMARY KEY,
  |  ARR_INT INTEGER [4]
  |);

This example will create a table with a field of the array type consisting of four integers. The subscripts of this array are from 1 to 4.

  |'[' <lower>:<upper> ']'

  |CREATE TABLE SAMPLE_ARR2 (
  |  ID INTEGER NOT NULL PRIMARY KEY,
  |  ARR_INT INTEGER [0:3, 0:3]
  |);

   |CREATE OR ALTER PROCEDURE SHOW_LANGS (
   |  CODE VARCHAR(5),
   |  GRADE SMALLINT,
   |  CTY VARCHAR(15))
   |RETURNS (LANGUAGES VARCHAR(15))
   |AS
   |  DECLARE VARIABLE I INTEGER;
   |BEGIN
   |  I = 1;
   |  WHILE (I <= 5) DO
   |  BEGIN
   |    SELECT LANGUAGE_REQ[:I]
   |    FROM JOB
   |    WHERE (JOB_CODE = :CODE)
   |      AND (JOB_GRADE = :GRADE)
   |      AND (JOB_COUNTRY = :CTY)
   |      AND (LANGUAGE_REQ IS NOT NULL))
   |    INTO :LANGUAGES;
   | 
   |    IF (LANGUAGES = '') THEN
   |    /* PRINTS 'NULL' INSTEAD OF BLANKS */
   |      LANGUAGES = 'NULL';
   |    I = I +1;
   |    SUSPEND;
   |  END
   |END