Tom Lane <t...@sss.pgh.pa.us> wrote: > Look under "computed fields" in the index ... looks like it's > towards the bottom of 34.4.2 in the 8.3 docs. > http://www.postgresql.org/docs/8.3/static/xfunc-sql.html#AEN40267 > > I had thought it was mentioned somewhere in chapter 4 as well, but > am not seeing it there right now. It's used in an example in 34.4.2 without a lot of definition. From experimenting a bit, it appears that when referencing a composite data value, any function which can take as its only parameter an instance of that composite type can be used as though it were a field name. This includes user functions written in any language, as well as built-in aggregates (and presumably any other functions which accept a composite type as the only parameter). Is that correct? Any restrictions or exceptions? (I assume that they are only allowed to retrieve values -- it doesn't seem like it would make sense to SET a value into such a "computed field".) It's clearly not particular to SQL functions, so it deserves mention outside of the context you referenced. Chapter 4 does seem like a good place. Under Column References or Function Calls (or both)? -Kevin
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