Substrait (substrait.io) is trying to be a backend independent plan representation. In practice, SQL dialects consist of a collection of functions in addition

Substrait (substrait.io) is trying to be a backend independent plan representation. In practice, SQL dialects consist of a collection of functions in addition to standard operators. These functions have varying naming, functionality, and edge case behavior -- often conflicting. Papering over this is a difficult problem. From a SQL database point of view, the SQL interface is well tested and required by end users. Adding an additional, rarely used interface to get to expose the same functionality is of questionable value. Using SQL as the plan serialization works pretty well.