<< ALTER EXTERNAL FUNCTION | FB 2.5 Language Reference | INDEX >>
<< ALTER EXTERNAL FUNCTION | FB 2.1 Language Reference | INDEX >>
<< DECLARE EXTERNAL FUNCTION | FB 2.0 Language Reference | DROP GENERATOR >>

DECLARE FILTER

Available in: DSQL, ESQL

Changed in: 2.0

Description

Makes a blob filter known to the database.

Syntax''' _

 DECLARE FILTER filtername
    INPUT_TYPE <sub_type> OUTPUT_TYPE <subtype>
    ENTRY_POINT 'function_name' MODULE_NAME 'library_name'

 <sub_type> ::= number | <mnemonic>

 <mnemonic> ::= binary | text | blr | acl | ranges | summary | format
                | transaction_description | external_file_description 
                | user_defined
  • In Firebird 2 and up, no two blob filters in a database may have the same combination of input and output type. Declaring a filter with an already existing input-output type combination will fail. Restoring pre-2.0 databases that contain such "duplicate" filters will also fail.
  • The possibility to indicate the blob types with their mnemonics instead of numbers was added in Firebird 2. The binary mnemonic for subtype 0 was also added in Firebird 2. The predefined mnemonics are case-insensitive.

Example

 declare filter Funnel
    input_type blr output_type text
    entry_point 'blr2asc' module_name 'myfilterlib'

User-defined mnemonics: If you want to define mnemonics for your own blob subtypes, you can add them to the RDB$TYPES system table as shown below. Once committed, the mnemonics can be used in subsequent filter declarations.

 insert into rdb$types (rdb$field_name, rdb$type, rdb$type_name)
   values ('RDB$FIELD_SUB_TYPE', -33, 'MIDI')

The value for rdb$field_name must always be 'RDB$FIELD_SUB_TYPE'. If you define your mnemonics in all-uppercase, you can use them case-insensitively and unquoted in your filter declarations.

See also:
DROP FILTER
Blob filter

back to top of page
<< ALTER EXTERNAL FUNCTION | FB 2.5 Language Reference | INDEX >>
<< ALTER EXTERNAL FUNCTION | FB 2.1 Language Reference | INDEX >>
<< DECLARE EXTERNAL FUNCTION | FB 2.0 Language Reference | DROP GENERATOR >>