I have been in contact with Flink and Calcite for a while, and I have some
questions about this issue:
https://issues.apache.org/jira/browse/FLINK-22848.
First of all, the discussion about this issue mentioned that since calcite
did not support the syntax analysis of set a=b (without quotes), regular
expressions were used. However, I checked the commit history some days ago,
and I found that calcite should already support SET syntax parsing (see
SqlSetOption) in v1.14 or even earlier. but its problem is that it would
recognize the `true/false/unknown/null` tokens as keywords, causing the
parsing to be worse than expected, but this problem can be solved by
restricting the syntax, like use '' in the issue FLINK-22848
<https://issues.apache.org/jira/browse/FLINK-22848>.
Then I investigated the earliest version of flink that introduced calcite,
flink should have introduced Calcite 1.16 in 1.5 at the earliest version.
At that time, calcite should already support the syntax of SET a=b (without
quotes), so I would like to find out What exactly does the "not supported"
mentioned in the issue FLINK-22848
<https://issues.apache.org/jira/browse/FLINK-22848> means? Maybe you can
give a more specific case.
In addition, I also have some doubts about the results of the discussion of
the issue. I think it is indeed a more elegant solution to use the SQL
parser to analyze it, but When calcite has built-in support for SET
grammar, why do we need to extend the SET grammar to re-support it? Even
this change may cause backward-incompatible.
In my personal opinion of view, is that we can solve this problem by adding
special restrictions on the above tokens on the basis of native Calcite
analysis, such as in the user manual because values such as `unknown` and
`null` are meaningless in the production environment.
