External functions for converting BLOB types are stored in dynamic libraries and loaded when necessary.

    For more details on BLOB subtypes, see .

    5.10.1. DECLARE FILTER

    Used for

    Declaring a BLOB filter to the database

    Available in

    DSQL, ESQL

    Syntax

    The DECLARE FILTER statement makes a BLOB filter available to the database. The name of the BLOB filter must be unique among the names of BLOB filters.

    Specifying the Subtypes

    The subtypes can be specified as the subtype number or as the subtype mnemonic name. Custom subtypes must be represented by negative numbers (from -1 to -32,768). An attempt to declare more than one BLOB filter with the same combination of the input and output types will fail with an error.

    INPUT_TYPE

    clause defining the BLOB subtype of the object to be converted

    OUTPUT_TYPE

    clause defining the BLOB subtype of the object to be created.

    Parameters

    ENTRY_POINT

    clause defining the name of the entry point (the name of the imported function) in the module.

    The clause defining the name of the module where the exported function is located. By default, modules must be located in the UDF folder of the root directory on the server. The UDFAccess parameter in firebird.conf allows editing of access restrictions to filter libraries.

    Examples of FILTER

    1. Creating a BLOB filter using subtype mnemonic names.

      1. DECLARE FILTER FUNNEL
      2.   INPUT_TYPE blr OUTPUT_TYPE text

    See also

    DROP FILTER

    5.10.2. DROP FILTER

    Used for

    Removing a BLOB filter declaration from the database

    Available in

    DSQL, ESQL

    Syntax

    The DROP FILTER statement removes the declaration of a BLOB filter from the database. Removing a BLOB filter from a database makes it unavailable for use from that database. The dynamic library where the conversion function is located remains intact and the removal from one database does not affect other databases in which the same BLOB filter is still declared.

    Any user connected to the database can drop a BLOB filter.

    Example

    Deleting a BLOB filter.

    1. DROP FILTER DESC_FILTER;

    See also