ClickHouse/dbms/src/Functions/multiIf.cpp

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#include <Functions/FunctionFactory.h>
#include <Functions/FunctionIfBase.h>
#include <Columns/ColumnNullable.h>
#include <Columns/ColumnConst.h>
#include <Columns/ColumnsNumber.h>
#include <Interpreters/castColumn.h>
#include <Common/typeid_cast.h>
#include <DataTypes/DataTypeNullable.h>
#include <DataTypes/getLeastSupertype.h>
namespace DB
{
namespace ErrorCodes
{
extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
}
/// Function multiIf, which generalizes the function if.
///
/// Syntax: multiIf(cond_1, then_1, ..., cond_N, then_N, else)
/// where N >= 1.
///
/// For all 1 <= i <= N, "cond_i" has type UInt8.
/// Types of all the branches "then_i" and "else" are either of the following:
/// - numeric types for which there exists a common type;
/// - dates;
/// - dates with time;
/// - strings;
/// - arrays of such types.
///
/// Additionally the arguments, conditions or branches, support nullable types
/// and the NULL value, with a NULL condition treated as false.
class FunctionMultiIf final : public FunctionIfBase</*null_is_false=*/true>
{
public:
static constexpr auto name = "multiIf";
static FunctionPtr create(const Context & context) { return std::make_shared<FunctionMultiIf>(context); }
FunctionMultiIf(const Context & context) : context(context) {}
public:
String getName() const override { return name; }
bool isVariadic() const override { return true; }
size_t getNumberOfArguments() const override { return 0; }
bool useDefaultImplementationForNulls() const override { return false; }
DataTypePtr getReturnTypeImpl(const DataTypes & args) const override
{
/// Arguments are the following: cond1, then1, cond2, then2, ... condN, thenN, else.
auto for_conditions = [&args](auto && f)
{
size_t conditions_end = args.size() - 1;
for (size_t i = 0; i < conditions_end; i += 2)
f(args[i]);
};
auto for_branches = [&args](auto && f)
{
size_t branches_end = args.size();
for (size_t i = 1; i < branches_end; i += 2)
f(args[i]);
f(args.back());
};
if (!(args.size() >= 3 && args.size() % 2 == 1))
throw Exception{"Invalid number of arguments for function " + getName(),
ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH};
/// Conditions must be UInt8, Nullable(UInt8) or Null. If one of conditions is Nullable, the result is also Nullable.
bool have_nullable_condition = false;
for_conditions([&](const DataTypePtr & arg)
{
const IDataType * nested_type;
if (arg->isNullable())
{
have_nullable_condition = true;
if (arg->onlyNull())
return;
const DataTypeNullable & nullable_type = static_cast<const DataTypeNullable &>(*arg);
nested_type = nullable_type.getNestedType().get();
}
else
{
nested_type = arg.get();
}
if (!WhichDataType(nested_type).isUInt8())
throw Exception{"Illegal type " + arg->getName() + " of argument (condition) "
"of function " + getName() + ". Must be UInt8.",
ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT};
});
DataTypes types_of_branches;
types_of_branches.reserve(args.size() / 2 + 1);
for_branches([&](const DataTypePtr & arg)
{
types_of_branches.emplace_back(arg);
});
DataTypePtr common_type_of_branches = getLeastSupertype(types_of_branches);
return have_nullable_condition
? makeNullable(common_type_of_branches)
: common_type_of_branches;
}
void executeImpl(Block & block, const ColumnNumbers & args, size_t result, size_t input_rows_count) override
{
/** We will gather values from columns in branches to result column,
* depending on values of conditions.
*/
struct Instruction
{
const IColumn * condition = nullptr;
const IColumn * source = nullptr;
bool condition_always_true = false;
bool condition_is_nullable = false;
bool source_is_constant = false;
};
std::vector<Instruction> instructions;
instructions.reserve(args.size() / 2 + 1);
Columns converted_columns_holder;
converted_columns_holder.reserve(instructions.size());
const DataTypePtr & return_type = block.getByPosition(result).type;
for (size_t i = 0; i < args.size(); i += 2)
{
Instruction instruction;
size_t source_idx = i + 1;
if (source_idx == args.size())
{
/// The last, "else" branch can be treated as a branch with always true condition "else if (true)".
--source_idx;
instruction.condition_always_true = true;
}
else
{
const ColumnWithTypeAndName & cond_col = block.getByPosition(args[i]);
/// We skip branches that are always false.
/// If we encounter a branch that is always true, we can finish.
if (cond_col.column->onlyNull())
continue;
if (cond_col.column->isColumnConst())
{
Field value = typeid_cast<const ColumnConst &>(*cond_col.column).getField();
if (value.isNull())
continue;
if (value.get<UInt64>() == 0)
continue;
instruction.condition_always_true = true;
}
else
{
if (cond_col.column->isColumnNullable())
instruction.condition_is_nullable = true;
instruction.condition = cond_col.column.get();
}
}
const ColumnWithTypeAndName & source_col = block.getByPosition(args[source_idx]);
if (source_col.type->equals(*return_type))
{
instruction.source = source_col.column.get();
}
else
{
/// Cast all columns to result type.
converted_columns_holder.emplace_back(castColumn(source_col, return_type, context));
instruction.source = converted_columns_holder.back().get();
}
if (instruction.source && instruction.source->isColumnConst())
instruction.source_is_constant = true;
instructions.emplace_back(std::move(instruction));
if (instructions.back().condition_always_true)
break;
}
size_t rows = input_rows_count;
MutableColumnPtr res = return_type->createColumn();
for (size_t i = 0; i < rows; ++i)
{
for (const auto & instruction : instructions)
{
bool insert = false;
if (instruction.condition_always_true)
insert = true;
else if (!instruction.condition_is_nullable)
insert = static_cast<const ColumnUInt8 &>(*instruction.condition).getData()[i];
else
{
const ColumnNullable & condition_nullable = static_cast<const ColumnNullable &>(*instruction.condition);
const ColumnUInt8 & condition_nested = static_cast<const ColumnUInt8 &>(condition_nullable.getNestedColumn());
const NullMap & condition_null_map = condition_nullable.getNullMapData();
insert = !condition_null_map[i] && condition_nested.getData()[i];
}
if (insert)
{
if (!instruction.source_is_constant)
res->insertFrom(*instruction.source, i);
else
res->insertFrom(static_cast<const ColumnConst &>(*instruction.source).getDataColumn(), 0);
break;
}
}
}
block.getByPosition(result).column = std::move(res);
}
private:
const Context & context;
};
void registerFunctionMultiIf(FunctionFactory & factory)
{
factory.registerFunction<FunctionMultiIf>();
/// These are obsolete function names.
factory.registerFunction<FunctionMultiIf>("caseWithoutExpr");
factory.registerFunction<FunctionMultiIf>("caseWithoutExpression");
}
}