Обсуждение: Row-wise Comparison
This is almost but not quite entirely unlike the NULL row issues Bruce has been raising lately. It is related to some infrastructure work I've been doing to fix some edge conditions I discovered (based on reviewing issues raised by Noah) with REFRESH MATERIALIZED VIEW CONCURRENTLY and also with work to implement incremental maintenance of materialized views. I intend to implement an operator for "rowvar is identical to rowvar", along with related operators to support merge joins based on this. It's actually done and pretty well tested, but needs documentation before I post the patch. I don't want to jump the gun on discussing details of that patch here, but ran into a problem when I went to write the docs, which is what I want *this* thread to be about. The docs in question are here, and actually discuss comparisons of what the SQL spec calls "row value constructors" and what the docs call row_constructors: http://www.postgresql.org/docs/devel/static/functions-comparisons.html#ROW-WISE-COMPARISON They don't begin to document things like this: test=# select pg_typeof(row(1, null::text)); pg_typeof ----------- record (1 row) test=# select row(1, null::text) = row(1, null::text); ?column? ---------- (1 row) test=# select pg_typeof(row(1, null::text)::record); pg_typeof ----------- record (1 row) test=# select row(1, null::text) = row(1, null::text)::record; ?column? ---------- t (1 row) The operators and sequencing involving actual records seems to be different from that for row value constructors, and it appears to be for good reason -- so that indexing will work correctly. My questions: Did I miss somewhere that the docs do cover this? If not, do we want to describe it? Why not? If we don't want to document the above, would the same arguments apply to the operators I'm adding? (i.e., Do we want to avoid docs on these, possibly on the basis of them being an internal implementation detail?) -- Kevin Grittner EDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
On Tue, Sep 10, 2013 at 02:32:56PM -0700, Kevin Grittner wrote: > The operators and sequencing involving actual records seems to be > different from that for row value constructors, and it appears to > be for good reason -- so that indexing will work correctly. > > My questions: > > Did I miss somewhere that the docs do cover this? I, too, don't see it. > If not, do we want to describe it? Why not? +1 for documenting it. We document <, >, <=, >=, =, and <> generically[1]. Several types that make non-obvious decisions for those operators (float8, range types, arrays) document those decisions. "record" hasn't done so, but it should. > If we don't want to document the above, would the same arguments > apply to the operators I'm adding? (i.e., Do we want to avoid docs > on these, possibly on the basis of them being an internal > implementation detail?) Separate decision, IMO. See progress on the more-recent thread. [1] http://www.postgresql.org/docs/9.3/static/functions-comparison.html -- Noah Misch EnterpriseDB http://www.enterprisedb.com