2010/12/17 Merlin Moncure <mmonc...@gmail.com> > On Fri, Dec 17, 2010 at 11:38 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > Pavel Stehule <pavel.steh...@gmail.com> writes: > >> 2010/12/17 Tom Lane <t...@sss.pgh.pa.us>: > >>> Furthermore, it's underspecified: who's to say how many dimensions of > >>> the array are supposed to get sliced off? There's no reasonable place > >>> to extend this syntax to specify that. It will also be inconsistent > >>> for "foreach scalar in array" to iterate element-by-element no matter > >>> how many dimensions array has, while "foreach array in array" does > >>> something different from that. > > > >> it reduce just one dimension. Now I expect, and I think so it is > >> correct, so user knows a used dimension. Just doesn't know a data. So > >> user can to decide and fill correct type. The design strictly remove > >> any U.I. from design. So using a incorect type is bug. > > > > In other words, your proposal is error-prone to use, restricted in what > > it can do, and incapable of being extended later without breaking > > things. If there is some redeeming social value to set against those > > problems, I'm not seeing it. > > > > What I think we should have is > > > > FOREACH scalar-variable IN ARRAY array-expression > > > > which iterates element by element regardless of how many dimensions the > > array has. Then there should be some other syntax for iterating over > > slices, and we should give some thought to being able to specify how > > "deep" the slice is. I can definitely think of use cases for pulling > > off either 1 dimension at a time (so you get vectors) or N-1 dimensions > > at a time, and it's not out of the realm of reason to want intermediate > > cases. > > > > Maybe > > > > FOR_EACH scalar-variable IN ARRAY array-expression > > > > FOR_SLICE array-variable [DEPTH n] IN ARRAY array-expression > > > > Or I guess you could use the same leading keyword if you make the depth > > specification mandatory for the slice case: > > > > FOREACH scalar-variable IN ARRAY array-expression > > > > FOREACH array-variable SLICE n IN ARRAY array-expression > > > > That might be a better idea since it avoids the inevitable argument over > > whether the default slice depth should be 1 dimension or N-1 dimensions. > > another way: > > FOREACH scalar IN ARRAY arr_exp DIMS in dim_var
> dim_var being int[], or possibly text, of length #dimensions, giving > per dimesion index. > If dim_var contains length it is need to be renamed: FOREACH scalar IN ARRAY arr_exp SIZES IN sizes_var. > > I like this because it would fit well with alternate form of unnest, > should it ever be written: > > create function unnest(anyarray, dims out int[], elem out anyelement) > returns setof... > > SLICE notation is still good though, and it's probably faster since > you have less work to do in iteration step? It's certainly easier, > but very plpgsql specific. > > merlin > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers > -- // Dmitriy.
