From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Mike Martin <redtux1(at)gmail(dot)com> |
Cc: | pgsql-sql <pgsql-sql(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Weird issue with truncation of values in array with some tables |
Date: | 2020-08-16 17:12:50 |
Message-ID: | 989596.1597597970@sss.pgh.pa.us |
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Lists: | pgsql-sql |
Mike Martin <redtux1(at)gmail(dot)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
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