fn merge_op_for_aggregate_expr(
aggr_expr: &Expr,
input_schema: &DFSchema,
) -> Result<IncrementalAggregateMergeOp, String>fn merge_op_for_aggregate_expr(
aggr_expr: &Expr,
input_schema: &DFSchema,
) -> Result<IncrementalAggregateMergeOp, String>