DECLARE FILTER
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DECLARE FILTER
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
binarymnemonic 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
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<< 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 >>
