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Add defaultValueOfTypeName

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This commit is contained in:
hcz 2020-08-19 14:44:11 +08:00
parent 898e19e18d
commit 4bbcec3d33
2 changed files with 71 additions and 0 deletions
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69
src/Functions/defaultValueOfTypeName.cpp Normal file
View File

@ -0,0 +1,69 @@
#include <Functions/IFunctionImpl.h>
#include <Functions/FunctionFactory.h>
#include <Core/Field.h>
#include <Columns/ColumnConst.h>
#include <DataTypes/DataTypeFactory.h>
namespace DB
{
namespace ErrorCodes
{
extern const int ILLEGAL_COLUMN;
}
/// Returns global default value for type name (example: 0 for numeric types, '' for String).
class FunctionDefaultValueOfTypeName : public IFunction
{
public:
static constexpr auto name = "defaultValueOfTypeName";
static FunctionPtr create(const Context &)
{
return std::make_shared<FunctionDefaultValueOfTypeName>();
}
String getName() const override
{
return name;
}
bool useDefaultImplementationForNulls() const override { return false; }
bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
size_t getNumberOfArguments() const override
{
return 1;
}
DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
{
auto col_type_const = typeid_cast<const ColumnConst *>(arguments.front().column.get());
if (!col_type_const || !isString(arguments.front().type))
throw Exception("The argument of function " + getName() + " must be a constant string describing type. "
"Instead there is a column with the following structure: " + arguments.front().column->dumpStructure(),
ErrorCodes::ILLEGAL_COLUMN);
return DataTypeFactory::instance().get(col_type_const->getValue<String>());
}
void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) const override
{
const IDataType & type = *block.getByPosition(arguments[0]).type;
block.getByPosition(result).column = type.createColumnConst(input_rows_count, type.getDefault());
}
ColumnPtr getResultIfAlwaysReturnsConstantAndHasArguments(const Block & block, const ColumnNumbers & arguments) const override
{
const IDataType & type = *block.getByPosition(arguments[0]).type;
return type.createColumnConst(1, type.getDefault());
}
};
void registerFunctionDefaultValueOfTypeName(FunctionFactory & factory)
{
factory.registerFunction<FunctionDefaultValueOfTypeName>();
}
}

2
src/Functions/registerFunctionsMiscellaneous.cpp
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@ -18,6 +18,7 @@ void registerFunctionBlockSerializedSize(FunctionFactory &);
void registerFunctionToColumnTypeName(FunctionFactory &);
void registerFunctionDumpColumnStructure(FunctionFactory &);
void registerFunctionDefaultValueOfArgumentType(FunctionFactory &);
void registerFunctionDefaultValueOfTypeName(FunctionFactory &);
void registerFunctionBlockSize(FunctionFactory &);
void registerFunctionBlockNumber(FunctionFactory &);
void registerFunctionRowNumberInBlock(FunctionFactory &);
@ -79,6 +80,7 @@ void registerFunctionsMiscellaneous(FunctionFactory & factory)
registerFunctionToColumnTypeName(factory);
registerFunctionDumpColumnStructure(factory);
registerFunctionDefaultValueOfArgumentType(factory);
registerFunctionDefaultValueOfTypeName(factory);
registerFunctionBlockSize(factory);
registerFunctionBlockNumber(factory);
registerFunctionRowNumberInBlock(factory);