Hi julian,thanks for your reply,I have got your point,and I agree with you.
Best, LakeShen Julian Hyde <[email protected]> 于2023年8月9日周三 09:59写道： > It substitutes a named data set for a table. > > We added it to support SQLstream, a streaming SQL system. When developing > streaming queries, it was sometimes convenient to substitute a table for a > stream, because the table had predictable results and didn’t need another > process inserting the rows. > > I don’t t think anyone is using this functionality, so in a dev branch [1] > I plan to remove the feature. See the commit 'Refactor: Remove TABLESAMPLE > SUBSTITUTE('name’)’. > > Julian > > [1] > https://github.com/apache/calcite/compare/main...julianhyde:calcite:xxxx-blackboard > > > > > > On Aug 8, 2023, at 4:27 AM, LakeShen <[email protected]> wrote: > > > > Hi all, > > > > Currently I see tablesample substitute('medium') in calcite's parser.jj > > file and some single tests, but I looked at the tablesample documentation > > for Postgresql and some other databases, Not seeing this SQL syntax, I > was > > wondering what exactly tablesample substitute('medium') means? > > At the same time,consider the following SQL: > > select * from product TABLESAMPLE SUBSTITUTE('medium') After the SqlNode > to > > RelNode, it also loses the TABLESAMPLE SUBSTITUTE('medium') information. > > Best, LakeShen > >
