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 >>
