Matthew Manuel wrote:
Hello, I found a strange error which occurs when I run a query from
PHP4, where if there is a column which has strings arbitrarily defined
text for all rows of a sub-select, and you attempt to sort by that
column, it cannot determine the type for that column in order to do the
sort.
I think it's actually a little more subtle than that, because of what
you're saying about psql.
- If you UNION more than one of these rows, the UNION seems to determine
the data type for the column, so the sort works. - If the values are
integers, the error does not occur
Yep - the UNION will coerce the "unknown" type, or give an error.
- if each arbitrary text value is explicitly cast, the error does not
occur. I have not tested other data types.
That's correct behaviour.
- This error does NOT occur when the query is run in the psql command line.
Now that puzzles me, since I get the error on the version I'm currently
logged into here (7.4.x). Could you just test it again?
query1: SELECT a.col1, a.col2 FROM (
SELECT 'test row' AS col1, 1 AS col2
) AS a
ORDER BY a.col1
Running...
*Warning*: pg_query(): Query failed: ERROR: failed to find conversion
function from "unknown" to text in */home3/manuel.ca/test/pgtest.php* on
line *14*
I don't suppose you could be running a locale of "C" in psql and
something else via php? I don't see how that could make the error go
away, but it's the only thing I can think of.
The heart of the problem is that the type is actually "unknown" and not
text. For example, if I had values '3 Jan 2005',' 3 Oct 2004' how should
they be sorted? Well, it depends on whether they are text or dates. How
does PG know which I want? It doesn't.
Actually, if we decide they are text then it depends on locale too,
since "C" locale will do a char-by-char sort whereas others will ignore
the leading space on the second example.
You can get similar problems with numeric literals if you want
floating-point or int8 instead of int4. PostgreSQL is flexible about its
types, but that does mean you need to be more precise in defining what
you mean sometimes.
HTH
--
Richard Huxton
Archonet Ltd
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