+1
On Wed, Jul 6, 2016 at 1:20 PM, Marcel Kornacker <[email protected]> wrote: > Could we then do the following: normalize all exprs <val>="" and > <val>=null to <val> is null, and then send through > HdfsPartitionPruner? > > On Wed, Jul 6, 2016 at 11:41 AM, Alex Behm <[email protected]> wrote: >> I think the main issue is that we need to preserve compatibility. >> z = "" should select the same partition(s) regardless of whether it is used >> in a single-clause or multi-clause DDL statement. >> My understanding is that today z = "" is equivalent to z IS NULL, so the >> same should be true for the new multi-clause DDL. >> >> >> >> >> On Wed, Jul 6, 2016 at 11:33 AM, Jim Apple <[email protected]> wrote: >> >>> In your opinion, in multi-clause DDL statements like >>> >>> alter table p partition (j<2 or j>0, k like "%", z = '') set uncached; >>> >>> Should "z = ''" be a synonym for "z IS NULL" like it is in the >>> single-clause DDL? >>> >>> On Wed, Jul 6, 2016 at 11:28 AM, Marcel Kornacker <[email protected]> >>> wrote: >>> > On Wed, Jul 6, 2016 at 10:20 AM, Jim Apple <[email protected]> wrote: >>> >> Let me try to explain what is going on here. >>> >> >>> >> Currently, if a user wants to specify a null partition for a DDL >>> >> operation, they write something like >>> >> >>> >> compute incremental stats incremental_null_part_key partition(p = NULL); >>> > >>> > We need to keep this working for the time being. >>> > >>> >> >>> >> For an empty string, they could write: >>> >> >>> >> alter table t_part drop partition (j=2, s='') >>> >> >>> >> This is unfortunate, as nothing "equals" NULL, and empty strings are >>> >> mapped to the NULL partition value. >>> >> >>> >> Amos has written a patch that allows DDL operations to work on more >>> >> than one partition at a time. These look like: >>> >> >>> >> alter table p partition (j<2 or j>0, k like "%") set uncached; >>> >> >>> >> Here, the clauses separated by commas are ANDed together to make one >>> >> clause. The question is whether these clauses, which now are clauses >>> >> and not just strangley-interpreted-equality, should keep the old >>> >> behavior or break existing queries. >>> > >>> > For these clauses we should use 'IS [NOT] NULL'. >>> > >>> >> >>> >> On Wed, Jul 6, 2016 at 6:44 AM, Amos Bird <[email protected]> wrote: >>> >>> This problem came from https://issues.cloudera.org/browse/IMPALA-1654 >>> , CR at https://gerrit.cloudera.org/#/c/1563/ . This patch will make >>> general predicates possible in most partition DDL operations. However, for >>> NULL partitions, the old KV way no longer works. Broken cases are <string >>> val>="" and <val>=null. This is due to the usage of HdfsPartitionPruner >>> which is used for Query time partition pruning. Should we keep the old way >>> of treating NULL partition as special cases? >>> >>> >>> >>> Amos >>>
