Thread: Weird issue with truncation of values in array with some tables
Hi
I have come across a weird issue with truncation of text in an array (in this case using pg_indexes view)
This query truncates the second array element at 63 characters
SELECT ARRAY[indexname,indexdef] FROM pg_indexes
However reversing the order doesn't truncate
SELECT ARRAY[indexdef,indexname] FROM pg_indexes
Anyone know why this behaviour occurs?
thanks
Mike
HiI have come across a weird issue with truncation of text in an array (in this case using pg_indexes view)This query truncates the second array element at 63 charactersSELECT ARRAY[indexname,indexdef] FROM pg_indexesHowever reversing the order doesn't truncateSELECT ARRAY[indexdef,indexname] FROM pg_indexesAnyone know why this behaviour occurs?
It's likely related to the following:
The system uses no more than NAMEDATALEN-1 bytes of an identifier; longer names can be written in commands, but they will be truncated. By default, NAMEDATALEN is 64 so the maximum identifier length is 63 bytes.
David J.
Mike Martin <redtux1@gmail.com> writes: > I have come across a weird issue with truncation of text in an array (in > this case using pg_indexes view) > This query truncates the second array element at 63 characters > SELECT ARRAY[indexname,indexdef] FROM pg_indexes > However reversing the order doesn't truncate > SELECT ARRAY[indexdef,indexname] FROM pg_indexes > Anyone know why this behaviour occurs? indexname is of type name, indexdef is of type text, and the rules for inferring the type of an array[] construct are such that the first element's type wins in these cases. regression=# SELECT pg_typeof(ARRAY[indexname,indexdef]) FROM pg_indexes limit 1; pg_typeof ----------- name[] (1 row) regression=# SELECT pg_typeof(ARRAY[indexdef,indexname]) FROM pg_indexes limit 1; pg_typeof ----------- text[] (1 row) You could insert an explicit cast to text to avoid the truncation of indexdef to name: regression=# SELECT pg_typeof(ARRAY[indexname::text,indexdef]) FROM pg_indexes limit 1; pg_typeof ----------- text[] (1 row) The documentation about that is here: https://www.postgresql.org/docs/current/typeconv-union-case.html although looking at this example it seems like that description isn't telling the full truth. regards, tom lane
Thanks!
Possibly the use of name type in pg_tables could be emphasized and maybe a note about name type in docs somewhere
On Sun, 16 Aug 2020, 18:12 Tom Lane, <tgl@sss.pgh.pa.us> wrote:
Mike Martin <redtux1@gmail.com> writes:
> I have come across a weird issue with truncation of text in an array (in
> this case using pg_indexes view)
> This query truncates the second array element at 63 characters
> SELECT ARRAY[indexname,indexdef] FROM pg_indexes
> However reversing the order doesn't truncate
> SELECT ARRAY[indexdef,indexname] FROM pg_indexes
> Anyone know why this behaviour occurs?
indexname is of type name, indexdef is of type text, and the rules
for inferring the type of an array[] construct are such that the
first element's type wins in these cases.
regression=# SELECT pg_typeof(ARRAY[indexname,indexdef]) FROM pg_indexes limit 1;
pg_typeof
-----------
name[]
(1 row)
regression=# SELECT pg_typeof(ARRAY[indexdef,indexname]) FROM pg_indexes limit 1;
pg_typeof
-----------
text[]
(1 row)
You could insert an explicit cast to text to avoid the truncation
of indexdef to name:
regression=# SELECT pg_typeof(ARRAY[indexname::text,indexdef]) FROM pg_indexes limit 1;
pg_typeof
-----------
text[]
(1 row)
The documentation about that is here:
https://www.postgresql.org/docs/current/typeconv-union-case.html
although looking at this example it seems like that description isn't
telling the full truth.
regards, tom lane