The new BLOB_APPEND function has a NULL behaviour that is not consistent
with the normal NULL behaviour. Using NULL in BLOB_APPEND behaves as an
empty string, while the normal behaviour for functions and operations
involving NULL is to result in NULL.
For example, normal concatenation:
select cast(null as blob sub_type text) || cast('a' as blob sub_type
text) || cast(null as blob sub_type text) || cast('b' as blob sub_type
text) from rdb$database;
results in NULL, while BLOB_APPEND:
select blob_append(null, 'a', null, 'b') from rdb$database;
results in 'ab'.
If the "normal" NULL-behaviour had been used, it would be possible to
easily rewrite normal concatenation involving blobs to BLOB_APPEND, but
now that requires careful consideration. In addition, this closes an
avenue for the engine to - at some point in the future, as an engine
optimization - rewrite concatenation to BLOB_APPEND internally.
Why was this NULL behaviour chosen?
Mark
--
Mark Rotteveel
Firebird-Devel mailing list, web interface at
https://lists.sourceforge.net/lists/listinfo/firebird-devel
