ClickHouse

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#include <Functions/IFunction.h>
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#include <Functions/FunctionFactory.h>
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#include <DataTypes/DataTypeString.h>
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#include <DataTypes/DataTypeNullable.h>
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#include <DataTypes/DataTypeDateTime.h>
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#include <Common/DateLUTImpl.h>
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#include <Core/Field.h>
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namespace DB
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{
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namespace ErrorCodes
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{
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    extern const int BAD_ARGUMENTS;
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}
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namespace
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{
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/** timezoneOf(x) - get the name of the timezone of DateTime data type.
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  * Example: Pacific/Pitcairn.
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  */
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class FunctionTimezoneOf : public IFunction
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{
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public:
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    static constexpr auto name = "timezoneOf";
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    String getName() const override { return name; }
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    static FunctionPtr create(ContextPtr) { return std::make_unique<FunctionTimezoneOf>(); }
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    size_t getNumberOfArguments() const override { return 1; }
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    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
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    DataTypePtr getReturnTypeImpl(const DataTypes & types) const override
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    {
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        DataTypePtr type_no_nullable = removeNullable(types[0]);
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        if (isDateTime(type_no_nullable) || isDateTime64(type_no_nullable))
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            return std::make_shared<DataTypeString>();
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        else
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            throw Exception(ErrorCodes::BAD_ARGUMENTS, "Bad argument for function {}, should be DateTime or DateTime64", name);
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    }
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    bool useDefaultImplementationForNulls() const override { return false; }
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    bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
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    ColumnNumbers getArgumentsThatDontImplyNullableReturnType(size_t /*number_of_arguments*/) const override { return {0}; }
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    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
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    {
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        DataTypePtr type_no_nullable = removeNullable(arguments[0].type);
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        return DataTypeString().createColumnConst(input_rows_count,
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            dynamic_cast<const TimezoneMixin &>(*type_no_nullable).getTimeZone().getTimeZone());
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    }
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    ColumnPtr getConstantResultForNonConstArguments(const ColumnsWithTypeAndName & arguments, const DataTypePtr &) const override
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    {
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        DataTypePtr type_no_nullable = removeNullable(arguments[0].type);
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        return DataTypeString().createColumnConst(1,
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            dynamic_cast<const TimezoneMixin &>(*type_no_nullable).getTimeZone().getTimeZone());
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    }
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};
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}
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REGISTER_FUNCTION(TimezoneOf)
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{
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    factory.registerFunction<FunctionTimezoneOf>();
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    factory.registerAlias("timeZoneOf", "timezoneOf");
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}
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}
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