feat: support function to_decimal(string).

src/query/functions/src/scalars/decimal.rs

@@ -17,11 +17,14 @@ use std::ops::*;
 use std::sync::Arc;
 
 use common_arrow::arrow::buffer::Buffer;
+use common_expression::read_decimal_with_size;
 use common_expression::types::decimal::*;
+use common_expression::types::string::StringColumn;
 use common_expression::types::*;
 use common_expression::with_integer_mapped_type;
 use common_expression::Column;
 use common_expression::ColumnBuilder;
+use common_expression::DecimalDeserializer;
 use common_expression::EvalContext;
 use common_expression::Function;
 use common_expression::FunctionDomain;
@@ -381,10 +384,12 @@ pub fn register(registry: &mut FunctionRegistry) {
         if args_type.len() != 1 {
             return None;
         }
-        if !args_type[0].is_decimal() && !args_type[0].is_numeric() {
+        if !matches!(
+            args_type[0],
+            DataType::Number(_) | DataType::Decimal(_) | DataType::String
+        ) {
             return None;
         }
-
         if params.len() != 2 {
             return None;
         }
@@ -468,13 +473,72 @@ fn convert_to_decimal(
     dest_type: DataType,
 ) -> Value<AnyType> {
     let arg = &args[0];
-    if from_type.is_integer() {
-        return integer_to_decimal(arg, ctx, from_type, dest_type);
+    match from_type {
+        DataType::Number(ty) => {
+            if ty.is_float() {
+                float_to_decimal(arg, ctx, from_type, dest_type)
+            } else {
+                integer_to_decimal(arg, ctx, from_type, dest_type)
+            }
+        }
+        DataType::Decimal(_) => decimal_to_decimal(arg, ctx, from_type, dest_type),
+        DataType::String => string_to_decimal(arg, ctx, from_type, dest_type),
+        _ => unreachable!("to_decimal not support this DataType"),
     }
-    if from_type.is_floating() {
-        return float_to_decimal(arg, ctx, from_type, dest_type);
+}
+
+fn string_to_decimal_internal<T: Decimal>(
+    ctx: &mut EvalContext,
+    string_column: &StringColumn,
+    size: DecimalSize,
+    dest_type: &DecimalDataType,
+) -> DecimalColumn {
+    let mut builder = DecimalDeserializer::<T>::with_capacity(dest_type, string_column.len());
+    for (row, buf) in string_column.iter().enumerate() {
+        match read_decimal_with_size::<T>(buf, size, true) {
+            Ok((d, _)) => builder.values.push(d),
+            Err(e) => {
+                ctx.set_error(row, format!("fail to decode string as decimal: {e}"));
+                builder.values.push(T::zero())
+            }
+        }
+    }
+    T::to_column(std::mem::take(&mut builder.values), size)
+}
+
+fn string_to_decimal(
+    arg: &ValueRef<AnyType>,
+    ctx: &mut EvalContext,
+    from_type: DataType,
+    dest_type: DataType,
+) -> Value<AnyType> {
+    let dest_type = dest_type.as_decimal().unwrap();
+
+    let mut is_scalar = false;
+    let column = match arg {
+        ValueRef::Column(column) => column.clone(),
+        ValueRef::Scalar(s) => {
+            is_scalar = true;
+            let builder = ColumnBuilder::repeat(s, 1, &from_type);
+            builder.build()
+        }
+    };
+    let string_column = StringType::try_downcast_column(&column).unwrap();
+    let result = match dest_type {
+        DecimalDataType::Decimal128(size) => {
+            string_to_decimal_internal::<i128>(ctx, &string_column, *size, dest_type)
+        }
+        DecimalDataType::Decimal256(size) => {
+            string_to_decimal_internal::<i256>(ctx, &string_column, *size, dest_type)
+        }
+    };
+
+    if is_scalar {
+        let scalar = result.index(0).unwrap();
+        Value::Scalar(Scalar::Decimal(scalar))
+    } else {
+        Value::Column(Column::Decimal(result))
     }
-    decimal_to_decimal(arg, ctx, from_type, dest_type)
 }
 
 fn integer_to_decimal(

src/query/functions/tests/it/scalars/testdata/array.txt

@@ -1756,7 +1756,7 @@ error:
   --> SQL:1:12
   |
 1 | array_sort(['x', 0, 1.2, 3.4, 5.6, 7.8])
-  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to cast type `String` to type `Decimal(2, 1)`
+  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ fail to decode string as decimal: Code: 1006, displayText = bad decimal literal: unexpected char. while evaluating function `to_decimal("x")`
 
 
 

tests/sqllogictests/suites/base/11_data_type/11_0006_data_type_decimal

@@ -1,3 +1,51 @@
+# 1e76 - 1
+query I
+select 9999999999999999999999999999999999999999999999999999999999999999999999999999;
+----
+9999999999999999999999999999999999999999999999999999999999999999999999999999
+
+# 1e76 - 1
+query I
+select -9999999999999999999999999999999999999999999999999999999999999999999999999999;
+----
+-9999999999999999999999999999999999999999999999999999999999999999999999999999
+
+query I
+select typeof(9999999999999999999999999999999999999999999999999999999999999999999999999999);
+----
+DECIMAL(76, 0)
+
+query I
+select typeof(-9999999999999999999999999999999999999999999999999999999999999999999999999999);
+----
+DECIMAL(76, 0)
+
+query I
+select typeof(999999999999999999999999999999999999999999999999999999999999999999999999999.9);
+----
+DECIMAL(76, 1)
+
+query I
+select typeof(1e76);
+----
+DOUBLE
+
+# 1e38 - 1
+query I
+select 99999999999999999999999999999999999999;
+----
+99999999999999999999999999999999999999
+
+query I
+select typeof(99999999999999999999999999999999999999);
+----
+DECIMAL(38, 0)
+
+query I
+select typeof(1e38);
+----
+DECIMAL(39, 0)
+
 statement ok
 drop table if exists t;
 
@@ -61,6 +109,13 @@ select 2::Decimal(2000, 3);
 statement error 1001
 select 20000::Decimal(4, 3);
 
+query I
+select '010.010'::decimal(6,4);
+----
+10.0100
+
+statement error 1001
+select '010.010'::decimal(5,4);
 
 ## tests from chatgpt
 ## some result should be modified if we parse 1.23 as Decimal instead of float by default, cc @yangsongfeng