Does sqlparser-rs support Left Semi/Left Anti/Right Semi/Right Anti Join ?

[mingmwang]

From the code based, looks like they are unsupported as of now.

https://github.com/sqlparser-rs/sqlparser-rs/blob/f7817bc7c257b6db76bb19b83033a7f2f001313b/src/ast/query.rs#L570-L581

[mingmwang]

@alamb

[Dandandan]

There is no specific syntax right now in sqlparser-rs indeed (most SQL dialects don't support it although some do).

[mingmwang]

Can we add those?

[alamb]

I think SQL queries typically don't have ANTI/SEMI joins directly -- instead they have correlated EXISTS and IN subqueries

Such correlated subqueries are typically implemented using various combinations of ANTI/SEMI joins as a performance optimization (rather than re-running each subquery )

What is the usecase of adding SEMI JOIN to the SQL grammar?

[mingmwang]

Some of the engines support ANTI/SEMI joins directly. And yesterday I found there was issue within DataFusions's RIGHT ANTI/RIGHT SEMI Join implementation and try to write some UTs to verify it, but found I can not just because those SQL syntaxes are not directly supported, and they are converted from other forms, which makes the UT writings not very straightforward.

[alamb]

I think if there is some precedent (like a reference to a sql dialect in sqlparser that supports syntax like SEMI JOIN, etc) we would definitely accept the PR

[mingmwang]

Apache Calcite:

https://github.com/apache/calcite/blob/main/site/_docs/algebra.md

SparkSQL

https://github.com/apache/spark/blob/5c43da6858721664318c3cdbcb051231b0e98175/sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBaseParser.g4#L708-L716