ClickHouse/src/DataTypes/DataTypeNothing.cpp at master · StackRadiusForks/ClickHouse

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#include <DataTypes/DataTypeNothing.h>

#include <DataTypes/Serializations/SerializationNothing.h>

#include <DataTypes/DataTypeFactory.h>

#include <Columns/ColumnNothing.h>

namespace DB

{

MutableColumnPtr DataTypeNothing::createColumn() const

{

return ColumnNothing::create(0);

}

bool DataTypeNothing::equals(const IDataType & rhs) const

{

return typeid(rhs) == typeid(*this);

}

SerializationPtr DataTypeNothing::doGetSerialization(const SerializationInfoSettings &) const

{

return SerializationNothing::create();

}

void registerDataTypeNothing(DataTypeFactory & factory)

{

factory.registerSimpleDataType("Nothing", [] { return DataTypePtr(std::make_shared<DataTypeNothing>()); }, DataTypeFactory::Case::Sensitive, Documentation{

.description = R"DOCS_MD(

The only purpose of this data type is to represent cases where a value is not expected. So you can't create a `Nothing` type value.

For example, literal [NULL](/sql-reference/syntax#null) has type of `Nullable(Nothing)`. See more about [Nullable](../../../sql-reference/data-types/nullable.md).

The `Nothing` type can also used to denote empty arrays:

```sql

SELECT toTypeName(array())

```

```text

┌─toTypeName(array())─┐

│ Array(Nothing) │

└─────────────────────┘

```

)DOCS_MD",

.syntax = "Nothing",

.examples = {},

.related = {},

});

}

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