[FLINK-11890] Replace Table API string-based expressions by a Java DSL - ASF JIRA

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Details

Type: New Feature
Status: Closed
Priority: Major
Resolution: Implemented
Affects Version/s: None
Fix Version/s: None
Component/s: Table SQL / API
Labels:
None

Description

Currently, expressions in the Table API can be defined in two ways. Either via the implicit Scala DSL or via custom strings:

Table revenue = orders
  .filter("cCountry === 'FRANCE'")
  .groupBy("cID, cName")
  .select("cID, cName, revenue.sum AS revSum");

// vs.

val revenue = orders
  .filter('cCountry === "FRANCE")
  .groupBy('cID, 'cName)
  .select('cID, 'cName, 'revenue.sum AS 'revSum)

The Java version of the Table API was always treated as a third class citizen.

In the past the string-based expression parser was/is:

multiple times out of sync with the Scala DSL
buggy because it was not properly tested
it blows up the API as every method must accept both representations like select(String) and select(Expression)
confusing for users because it looks like SQL but is actually only SQL-like
does not provide JavaDocs or further help in case of parse errors within the IDE, a user can only consult the online documentation

We should discuss alternatives for the string-based expressions and might come up with a DSL-like approach to make the Table API ready for the future.

This issue would be a big design shift for Table API users in Java. We need to discuss if the benefits are worth the change. A first proof-of-concept/design proposal will follow shortly.