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 <blobtype> OUTPUT_TYPE <blobtype>
   ENTRY_POINT 'function_name' MODULE_NAME 'library_name'

<blobtype>  ::=  number | <mnemonic>
<mnemonic>  ::=  binary | text | blr | acl | ranges | summary | format
                 | transaction_description | external_file_description
The possibility to indicate the BLOB types with mnemonics instead of numbers was 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'

Tip

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.