colon `:` operator - initial implementation

[Samyak2]

Context

Discussion started here - #2 (comment) (see next few comments too).

The colon operator is a shorthand for variant_get. For example, variant_get(column, '$.field', 'int') can be written as column:field::int. The part after the colon is a JSON path.

Implementation

• The first major blocker was the fact that the parser did not understand : as an operator.
  • It is supported in the snowflake dialect of datafusion-sqlparser-rs, but datafusion uses the generic dialect.
  • Some initial exploration was done here: epic: Initial implementation of this crate #2 (comment)
  • I have a PR for this in the parser here: GenericDialect: support colon operator for JsonAccess apache/datafusion-sqlparser-rs#2124
• Use ExprPlanner to allow : as a custom operator from this crate. See: epic: Initial implementation of this crate #2 (comment)
• The actual implementation of the operator - which would simply call the same function as variant_get.

References

• Databricks documentation on : - https://docs.databricks.com/aws/en/sql/language-manual/functions/colonsign (note: their colon works on JSON strings too, but we would be focusing on variant in this case)
• A blog post I had authored on variant: https://www.e6data.com/blog/faster-json-sql-variant-data-type