I see... PostgreSQL wants to guess the datatype, given no clear syntactic information, and perhaps a varchar(n) wouldn't be a valid cast to some of the possible datatypes.
So, where x = '(1,2)' might be legal for comparing to x, but a field of type varchar(5) might not be, as in where x = y, where y is type varchar(5) containing '(1,2)'. (Time values don't have this problem in pure ANSI SQL, since the literal is TIME '12:34', but I can see for user types it might be ambiguous). I find PostgreSQL's handling of this strange, as I come from systems where 'xxx' is either a varchar or char type, in all contexts, and implicit casts handle any needed conversions. But now I understand why it does things this way. Thanks. -----Original Message----- From: Tom Lane [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 9:50 PM To: Chuck McDevitt Cc: Andrew Hammond; Josh Berkus; pgsql-hackers@postgresql.org; Dann Corbit; Larry McGhaw Subject: Re: [HACKERS] Selecting a constant question: A summary "Chuck McDevitt" <[EMAIL PROTECTED]> writes: > Just a curiosity question: Why is the type of a literal '1' "unknown" > instead of varchar(1)? Because, for instance, it might be intended as an integer or float or numeric value. Change the content a little, like '(1,2)' or '12:34', and maybe it's a point or time value. There are plenty of contexts in which the intended type of a literal is obviously not text/varchar. We assign unknown initially as a way of flagging that the type assignment is uncertain. Once we have a value that we think is varchar (a table column for instance), the rules for deciding to cast it to a different type get a lot more stringent. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
