Merge pull request #52520 from zvonand/revert-52450-remove-to-decimal…

…-string Fix `toDecimalString` function
ClickHouse · Jul 26, 2023 · 7bcef0a · 7bcef0a
2 parents 3387b02 + 4f7bdf3
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diff --git a/docs/en/sql-reference/functions/type-conversion-functions.md b/docs/en/sql-reference/functions/type-conversion-functions.md
@@ -945,6 +945,44 @@ Result:
 └────────────┴───────┘
 ```
 
+## toDecimalString
+
+Converts a numeric value to String with the number of fractional digits in the output specified by the user.
+
+**Syntax**
+
+``` sql
+toDecimalString(number, scale)
+```
+
+**Parameters**
+
+- `number` — Value to be represented as String, [Int, UInt](/docs/en/sql-reference/data-types/int-uint.md), [Float](/docs/en/sql-reference/data-types/float.md), [Decimal](/docs/en/sql-reference/data-types/decimal.md),
+- `scale` — Number of fractional digits, [UInt8](/docs/en/sql-reference/data-types/int-uint.md).
+    * Maximum scale for [Decimal](/docs/en/sql-reference/data-types/decimal.md) and [Int, UInt](/docs/en/sql-reference/data-types/int-uint.md) types is 77 (it is the maximum possible number of significant digits for Decimal),
+    * Maximum scale for [Float](/docs/en/sql-reference/data-types/float.md) is 60.
+
+**Returned value**
+
+- Input value represented as [String](/docs/en/sql-reference/data-types/string.md) with given number of fractional digits (scale).
+    The number is rounded up or down according to common arithmetic in case requested scale is smaller than original number's scale.
+
+**Example**
+
+Query:
+
+``` sql
+SELECT toDecimalString(CAST('64.32', 'Float64'), 5);
+```
+
+Result:
+
+```response
+┌toDecimalString(CAST('64.32', 'Float64'), 5)─┐
+│ 64.32000                                    │
+└─────────────────────────────────────────────┘
+```
+
 ## reinterpretAsUInt(8\|16\|32\|64)
 
 ## reinterpretAsInt(8\|16\|32\|64)

diff --git a/docs/ru/sql-reference/functions/type-conversion-functions.md b/docs/ru/sql-reference/functions/type-conversion-functions.md
@@ -762,6 +762,44 @@ SELECT toFixedString('foo\0bar', 8) AS s, toStringCutToZero(s) AS s_cut;
 └────────────┴───────┘
 ```
 
+## toDecimalString
+
+Принимает любой численный тип первым аргументом, возвращает строковое десятичное представление числа с точностью, заданной вторым аргументом.
+
+**Синтаксис**
+
+``` sql
+toDecimalString(number, scale)
+```
+
+**Параметры**
+
+-   `number` — Значение любого числового типа: [Int, UInt](/docs/ru/sql-reference/data-types/int-uint.md), [Float](/docs/ru/sql-reference/data-types/float.md), [Decimal](/docs/ru/sql-reference/data-types/decimal.md),
+-   `scale` — Требуемое количество десятичных знаков после запятой, [UInt8](/docs/ru/sql-reference/data-types/int-uint.md).
+    * Значение `scale` для типов [Decimal](/docs/ru/sql-reference/data-types/decimal.md) и [Int, UInt](/docs/ru/sql-reference/data-types/int-uint.md) должно не превышать 77 (так как это наибольшее количество значимых символов для этих типов),
+    * Значение `scale` для типа [Float](/docs/ru/sql-reference/data-types/float.md) не должно превышать 60.
+
+**Возвращаемое значение**
+
+-   Строка ([String](/docs/en/sql-reference/data-types/string.md)), представляющая собой десятичное представление входного числа с заданной длиной дробной части.
+    При необходимости число округляется по стандартным правилам арифметики.
+
+**Пример использования**
+
+Запрос:
+
+``` sql
+SELECT toDecimalString(CAST('64.32', 'Float64'), 5);
+```
+
+Результат:
+
+```response
+┌─toDecimalString(CAST('64.32', 'Float64'), 5)┐
+│ 64.32000                                    │
+└─────────────────────────────────────────────┘
+```
+
 ## reinterpretAsUInt(8\|16\|32\|64) {#reinterpretasuint8163264}
 
 ## reinterpretAsInt(8\|16\|32\|64) {#reinterpretasint8163264}

diff --git a/src/Functions/FunctionToDecimalString.cpp b/src/Functions/FunctionToDecimalString.cpp
@@ -0,0 +1,22 @@
+#include <Functions/FunctionFactory.h>
+#include <Functions/FunctionToDecimalString.h>
+#include <Functions/IFunction.h>
+
+namespace DB
+{
+
+REGISTER_FUNCTION(ToDecimalString)
+{
+    factory.registerFunction<FunctionToDecimalString>(
+        FunctionDocumentation{
+            .description=R"(
+Returns string representation of a number. First argument is the number of any numeric type,
+second argument is the desired number of digits in fractional part. Returns String.
+
+        )",
+            .examples{{"toDecimalString", "SELECT toDecimalString(2.1456,2)", ""}},
+            .categories{"String"}
+        }, FunctionFactory::CaseInsensitive);
+}
+
+}
diff --git a/src/Functions/FunctionToDecimalString.h b/src/Functions/FunctionToDecimalString.h
@@ -0,0 +1,262 @@
+#pragma once
+
+#include <Core/Types.h>
+#include <Core/DecimalFunctions.h>
+#include <Functions/IFunction.h>
+#include <Functions/FunctionHelpers.h>
+#include <Columns/ColumnsNumber.h>
+#include <Columns/ColumnString.h>
+#include <Columns/ColumnVector.h>
+#include <Columns/ColumnDecimal.h>
+#include <DataTypes/DataTypeString.h>
+#include <DataTypes/DataTypesNumber.h>
+#include <IO/WriteBufferFromVector.h>
+#include <IO/WriteHelpers.h>
+#include <Interpreters/Context_fwd.h>
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int ILLEGAL_COLUMN;
+    extern const int CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER;
+}
+
+class FunctionToDecimalString : public IFunction
+{
+public:
+    static constexpr auto name = "toDecimalString";
+    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionToDecimalString>(); }
+
+    String getName() const override { return name; }
+
+    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return true; }
+
+    size_t getNumberOfArguments() const override { return 2; }
+
+    DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
+    {
+        FunctionArgumentDescriptors mandatory_args = {
+            {"Value", &isNumber<IDataType>, nullptr, "Number"},
+            {"precision", &isNativeInteger<IDataType>, &isColumnConst, "const Integer"}
+        };
+
+        validateFunctionArgumentTypes(*this, arguments, mandatory_args, {});
+
+        return std::make_shared<DataTypeString>();
+    }
+
+    bool useDefaultImplementationForConstants() const override { return true; }
+
+private:
+    /// For operations with Integer/Float
+    template <typename FromVectorType>
+    void vectorConstant(const FromVectorType & vec_from, UInt8 precision,
+                        ColumnString::Chars & vec_to, ColumnString::Offsets & result_offsets) const
+    {
+        size_t input_rows_count = vec_from.size();
+        result_offsets.resize(input_rows_count);
+
+        /// Buffer is used here and in functions below because resulting size cannot be precisely anticipated,
+        /// and buffer resizes on-the-go. Also, .count() provided by buffer is convenient in this case.
+        WriteBufferFromVector<ColumnString::Chars> buf_to(vec_to);
+
+        for (size_t i = 0; i < input_rows_count; ++i)
+        {
+            format(vec_from[i], buf_to, precision);
+            result_offsets[i] = buf_to.count();
+        }
+
+        buf_to.finalize();
+    }
+
+    template <typename FirstArgVectorType>
+    void vectorVector(const FirstArgVectorType & vec_from, const ColumnVector<UInt8>::Container & vec_precision,
+                      ColumnString::Chars & vec_to, ColumnString::Offsets & result_offsets) const
+    {
+        size_t input_rows_count = vec_from.size();
+        result_offsets.resize(input_rows_count);
+
+        WriteBufferFromVector<ColumnString::Chars> buf_to(vec_to);
+
+        constexpr size_t max_digits = std::numeric_limits<UInt256>::digits10;
+
+        for (size_t i = 0; i < input_rows_count; ++i)
+        {
+            if (vec_precision[i] > max_digits)
+                throw DB::Exception(DB::ErrorCodes::CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER,
+                                    "Too many fractional digits requested, shall not be more than {}", max_digits);
+            format(vec_from[i], buf_to, vec_precision[i]);
+            result_offsets[i] = buf_to.count();
+        }
+
+        buf_to.finalize();
+    }
+
+    /// For operations with Decimal
+    template <typename FirstArgVectorType>
+    void vectorConstant(const FirstArgVectorType & vec_from, UInt8 precision,
+                        ColumnString::Chars & vec_to, ColumnString::Offsets & result_offsets, UInt8 from_scale) const
+    {
+        /// There are no more than 77 meaning digits (as it is the max length of UInt256). So we can limit it with 77.
+        constexpr size_t max_digits = std::numeric_limits<UInt256>::digits10;
+        if (precision > max_digits)
+            throw DB::Exception(DB::ErrorCodes::CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER,
+                                "Too many fractional digits requested for Decimal, must not be more than {}", max_digits);
+
+        WriteBufferFromVector<ColumnString::Chars> buf_to(vec_to);
+        size_t input_rows_count = vec_from.size();
+        result_offsets.resize(input_rows_count);
+
+        for (size_t i = 0; i < input_rows_count; ++i)
+        {
+            writeText(vec_from[i], from_scale, buf_to, true, true, precision);
+            writeChar(0, buf_to);
+            result_offsets[i] = buf_to.count();
+        }
+        buf_to.finalize();
+    }
+
+    template <typename FirstArgVectorType>
+    void vectorVector(const FirstArgVectorType & vec_from, const ColumnVector<UInt8>::Container & vec_precision,
+                      ColumnString::Chars & vec_to, ColumnString::Offsets & result_offsets, UInt8 from_scale) const
+    {
+        size_t input_rows_count = vec_from.size();
+        result_offsets.resize(input_rows_count);
+
+        WriteBufferFromVector<ColumnString::Chars> buf_to(vec_to);
+
+        constexpr size_t max_digits = std::numeric_limits<UInt256>::digits10;
+
+        for (size_t i = 0; i < input_rows_count; ++i)
+        {
+            if (vec_precision[i] > max_digits)
+                throw DB::Exception(DB::ErrorCodes::CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER,
+                                    "Too many fractional digits requested for Decimal, must not be more than {}", max_digits);
+            writeText(vec_from[i], from_scale, buf_to, true, true, vec_precision[i]);
+            writeChar(0, buf_to);
+            result_offsets[i] = buf_to.count();
+        }
+        buf_to.finalize();
+    }
+
+    template <is_floating_point T>
+    static void format(T value, DB::WriteBuffer & out, UInt8 precision)
+    {
+        /// Maximum of 60 is hard-coded in 'double-conversion/double-conversion.h' for floating point values,
+        /// Catch this here to give user a more reasonable error.
+        if (precision > 60)
+            throw DB::Exception(DB::ErrorCodes::CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER,
+                                "Too high precision requested for Float, must not be more than 60, got {}", Int8(precision));
+
+        DB::DoubleConverter<false>::BufferType buffer;
+        double_conversion::StringBuilder builder{buffer, sizeof(buffer)};
+
+        const auto result = DB::DoubleConverter<false>::instance().ToFixed(value, precision, &builder);
+
+        if (!result)
+            throw DB::Exception(DB::ErrorCodes::CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER, "Error processing number: {}", value);
+
+        out.write(buffer, builder.position());
+        writeChar(0, out);
+    }
+
+    template <is_integer T>
+    static void format(T value, DB::WriteBuffer & out, UInt8 precision)
+    {
+        /// Fractional part for Integer is just trailing zeros. Let's limit it with 77 (like with Decimals).
+        constexpr size_t max_digits = std::numeric_limits<UInt256>::digits10;
+        if (precision > max_digits)
+            throw DB::Exception(DB::ErrorCodes::CANNOT_PRINT_FLOAT_OR_DOUBLE_NUMBER,
+                                "Too many fractional digits requested, shall not be more than {}", max_digits);
+        writeText(value, out);
+        if (precision > 0) [[likely]]
+        {
+            writeChar('.', out);
+            for (int i = 0; i < precision; ++i)
+                writeChar('0', out);
+            writeChar(0, out);
+        }
+    }
+
+public:
+    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t /*input_rows_count*/) const override
+    {
+        switch (arguments[0].type->getTypeId())
+        {
+            case TypeIndex::UInt8:      return executeType<UInt8>(arguments);
+            case TypeIndex::UInt16:     return executeType<UInt16>(arguments);
+            case TypeIndex::UInt32:     return executeType<UInt32>(arguments);
+            case TypeIndex::UInt64:     return executeType<UInt64>(arguments);
+            case TypeIndex::UInt128:    return executeType<UInt128>(arguments);
+            case TypeIndex::UInt256:    return executeType<UInt256>(arguments);
+            case TypeIndex::Int8:       return executeType<Int8>(arguments);
+            case TypeIndex::Int16:      return executeType<Int16>(arguments);
+            case TypeIndex::Int32:      return executeType<Int32>(arguments);
+            case TypeIndex::Int64:      return executeType<Int64>(arguments);
+            case TypeIndex::Int128:     return executeType<Int128>(arguments);
+            case TypeIndex::Int256:     return executeType<Int256>(arguments);
+            case TypeIndex::Float32:    return executeType<Float32>(arguments);
+            case TypeIndex::Float64:    return executeType<Float64>(arguments);
+            case TypeIndex::Decimal32:  return executeType<Decimal32>(arguments);
+            case TypeIndex::Decimal64:  return executeType<Decimal64>(arguments);
+            case TypeIndex::Decimal128: return executeType<Decimal128>(arguments);
+            case TypeIndex::Decimal256: return executeType<Decimal256>(arguments);
+            default:
+                throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of argument of function {}",
+                                arguments[0].column->getName(), getName());
+        }
+    }
+
+private:
+    template <typename T>
+    ColumnPtr executeType(const ColumnsWithTypeAndName & arguments) const
+    {
+        const auto * precision_col = checkAndGetColumn<ColumnVector<UInt8>>(arguments[1].column.get());
+        const auto * precision_col_const = checkAndGetColumnConst<ColumnVector<UInt8>>(arguments[1].column.get());
+
+        auto result_col = ColumnString::create();
+        auto * result_col_string = assert_cast<ColumnString *>(result_col.get());
+        ColumnString::Chars & result_chars = result_col_string->getChars();
+        ColumnString::Offsets & result_offsets = result_col_string->getOffsets();
+
+        if constexpr (is_decimal<T>)
+        {
+            const auto * from_col = checkAndGetColumn<ColumnDecimal<T>>(arguments[0].column.get());
+            UInt8 from_scale = from_col->getScale();
+
+            if (from_col)
+            {
+                if (precision_col_const)
+                    vectorConstant(from_col->getData(), precision_col_const->template getValue<UInt8>(), result_chars, result_offsets, from_scale);
+                else if (precision_col)
+                    vectorVector(from_col->getData(), precision_col->getData(), result_chars, result_offsets, from_scale);
+                else
+                    throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of second argument of function formatDecimal", arguments[1].column->getName());
+            }
+            else
+                throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of first argument of function formatDecimal", arguments[0].column->getName());
+        }
+        else
+        {
+            const auto * from_col = checkAndGetColumn<ColumnVector<T>>(arguments[0].column.get());
+            if (from_col)
+            {
+                if (precision_col_const)
+                    vectorConstant(from_col->getData(), precision_col_const->template getValue<UInt8>(), result_chars, result_offsets);
+                else if (precision_col)
+                    vectorVector(from_col->getData(), precision_col->getData(), result_chars, result_offsets);
+                else
+                    throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of second argument of function formatDecimal", arguments[1].column->getName());
+
+            }
+            else
+                throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of first argument of function formatDecimal", arguments[0].column->getName());
+        }
+
+        return result_col;
+    }
+};
+
+}