Re: Bug #513: union all changes char(3) column definition

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Added to TODO:
> * CREATE TABLE AS can not determine column lengths from expressions
> Seems it should be documented. Do we throw an error in these cases?

No. What we do right now is to generate non-length-constrained column
types for the created table.

Your TODO item is too pessimistic: we *do* determine the column length
in simple cases. For example:

regression=# create table foo (f1 char(3));
CREATE
regression=# create table bar as select * from foo;
SELECT
regression=# \d bar
Table "bar"
Column | Type | Modifiers
--------+--------------+-----------
f1 | character(3) |

However, in more complex cases we don't know the column length:

regression=# create table baz as select f1 || 'z' as f1 from foo;
SELECT
regression=# \d baz
Table "baz"
Column | Type | Modifiers
--------+--------+-----------
f1 | bpchar |

The argument here is about how much intelligence it's reasonable to
expect the system to have. It's very clearly not feasible to derive
a length limit automagically in every case. How hard should we try?

regards, tom lane