Closed
Description
There are two known issues for current partition pruning implementation:
- it doesn't support filter conditions that can't be push down to datasource
- it doesn't support expressions that can't calculate range
Both of them are not reasonable.
@coocood advised in #6642 to ignore the selection node above datasoure node, so filter conditions that can't be push down to datasource won't be considered by partition pruning function, that's why limitation 1 exists.
Suppose we haven't implement timestamp type in TiKV yet, the filter condition will not be pushed down to datasource, then partition pruning can't work on this example:
select ts from t where ts > 20060308110502
Limitation 2 comes from the fact that we currently use range calculation to implement partition pruning.
create table t (id int) partition by range (to_days(id)) ...
select * from t where id > 2018-03-08
to_days is a function, we can't calculate range for it, so partition pruning can't work.