Convert approx_distinct to UDAF

Author: Lordworms

datafusion/expr/src/aggregate_function.rs

@@ -41,8 +41,6 @@ pub enum AggregateFunction {
     Max,
     /// Average
     Avg,
-    /// Approximate distinct function
-    ApproxDistinct,
     /// Aggregation into an array
     ArrayAgg,
     /// N'th value in a group according to some ordering
@@ -97,7 +95,6 @@ impl AggregateFunction {
             Min => "MIN",
             Max => "MAX",
             Avg => "AVG",
-            ApproxDistinct => "APPROX_DISTINCT",
             ArrayAgg => "ARRAY_AGG",
             NthValue => "NTH_VALUE",
             Correlation => "CORR",
@@ -160,7 +157,6 @@ impl FromStr for AggregateFunction {
             "regr_syy" => AggregateFunction::RegrSYY,
             "regr_sxy" => AggregateFunction::RegrSXY,
             // approximate
-            "approx_distinct" => AggregateFunction::ApproxDistinct,
             "approx_median" => AggregateFunction::ApproxMedian,
             "approx_percentile_cont" => AggregateFunction::ApproxPercentileCont,
             "approx_percentile_cont_with_weight" => {
@@ -198,9 +194,7 @@ impl AggregateFunction {
             })?;
 
         match self {
-            AggregateFunction::Count | AggregateFunction::ApproxDistinct => {
-                Ok(DataType::Int64)
-            }
+            AggregateFunction::Count => Ok(DataType::Int64),
             AggregateFunction::Max | AggregateFunction::Min => {
                 // For min and max agg function, the returned type is same as input type.
                 // The coerced_data_types is same with input_types.
@@ -261,9 +255,9 @@ impl AggregateFunction {
         // note: the physical expression must accept the type returned by this function or the execution panics.
         match self {
             AggregateFunction::Count => Signature::variadic_any(Volatility::Immutable),
-            AggregateFunction::ApproxDistinct
-            | AggregateFunction::Grouping
-            | AggregateFunction::ArrayAgg => Signature::any(1, Volatility::Immutable),
+            AggregateFunction::Grouping | AggregateFunction::ArrayAgg => {
+                Signature::any(1, Volatility::Immutable)
+            }
             AggregateFunction::Min | AggregateFunction::Max => {
                 let valid = STRINGS
                     .iter()

datafusion/expr/src/expr_fn.rs

@@ -266,24 +266,6 @@ pub fn in_list(expr: Expr, list: Vec<Expr>, negated: bool) -> Expr {
     Expr::InList(InList::new(Box::new(expr), list, negated))
 }
 
-/// Returns the approximate number of distinct input values.
-/// This function provides an approximation of count(DISTINCT x).
-/// Zero is returned if all input values are null.
-/// This function should produce a standard error of 0.81%,
-/// which is the standard deviation of the (approximately normal)
-/// error distribution over all possible sets.
-/// It does not guarantee an upper bound on the error for any specific input set.
-pub fn approx_distinct(expr: Expr) -> Expr {
-    Expr::AggregateFunction(AggregateFunction::new(
-        aggregate_function::AggregateFunction::ApproxDistinct,
-        vec![expr],
-        false,
-        None,
-        None,
-        None,
-    ))
-}
-
 /// Calculate an approximation of the median for `expr`.
 pub fn approx_median(expr: Expr) -> Expr {
     Expr::AggregateFunction(AggregateFunction::new(

datafusion/expr/src/type_coercion/aggregates.rs

@@ -96,9 +96,7 @@ pub fn coerce_types(
     check_arg_count(agg_fun.name(), input_types, &signature.type_signature)?;
 
     match agg_fun {
-        AggregateFunction::Count | AggregateFunction::ApproxDistinct => {
-            Ok(input_types.to_vec())
-        }
+        AggregateFunction::Count => Ok(input_types.to_vec()),
         AggregateFunction::ArrayAgg => Ok(input_types.to_vec()),
         AggregateFunction::Min | AggregateFunction::Max => {
             // min and max support the dictionary data type
@@ -539,7 +537,6 @@ mod tests {
         let funs = vec![
             AggregateFunction::Count,
             AggregateFunction::ArrayAgg,
-            AggregateFunction::ApproxDistinct,
             AggregateFunction::Min,
             AggregateFunction::Max,
         ];