On 05/03/2016 04:28 AM, Durumdara wrote:
Hello!
As I experienced, PGSQL changes the result field sizes to unlimited
varchar, when I passed different field size in same column of the union.
SP.Key - varchar(100)
SP.Value - varchar(200)
Example:
select 'a', value from sp
union all
select key, value from sp
The first field is not limited to 100, it's unlimited varchar() (= Text,
Memo, CLOB).
So PG don't use the maximal field size (100).
The maximum size of the unknown 'a' as text is unlimited so it did choose the maximum field size max(INF, 100) = 100
The system recognizes there is no guarantee that 'a' could be reliably casted into a varchar(100)
If I did cast on the field to resize to 100, the result is limited
correctly.
select cast('a' as varchar(100)), value from sp
union all
select key, value from sp
Can I force somehow to PG use the maximal size?
Or must I know and equalize all field sizes in union?
Or must I use temporary tables and inserts to not get this problem?
See below for complete explanation:
http://www.postgresql.org/docs/9.5/static/typeconv-union-case.html
10.5. UNION, CASE, and Related Constructs
This seems to fail to answer the OPs question. Specifically, do these rules automatically, or at least if #1 is not true, cause typemod information to be lost? IOW, is it because of the unknown that both end up up-casted to typemod-less text?
David J.
