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#include <DataTypes/DataTypeArray.h>
#include <DataTypes/getLeastSupertype.h>
#include <Functions/FunctionFactory.h>
namespace DB
{
namespace ErrorCodes
{
extern const int TOO_FEW_ARGUMENTS_FOR_FUNCTION;
}
namespace
{
/// Implements the CASE construction when it is
/// provided an expression. Users should not call this function.
class FunctionCaseWithExpression : public IFunction
{
public:
static constexpr auto name = "caseWithExpression";
static FunctionPtr create(ContextPtr context_) { return std::make_shared<FunctionCaseWithExpression>(context_); }
explicit FunctionCaseWithExpression(ContextPtr context_) : context(context_) {}
bool isVariadic() const override { return true; }
bool useDefaultImplementationForConstants() const override { return false; }
bool useDefaultImplementationForNulls() const override { return false; }
bool useDefaultImplementationForNothing() const override { return false; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
size_t getNumberOfArguments() const override { return 0; }
String getName() const override { return name; }
DataTypePtr getReturnTypeImpl(const DataTypes & args) const override
{
if (args.empty())
throw Exception(ErrorCodes::TOO_FEW_ARGUMENTS_FOR_FUNCTION, "Function {} expects at least 1 arguments", getName());
/// See the comments in executeImpl() to understand why we actually have to
/// get the return type of a transform function.
/// Get the types of the arrays that we pass to the transform function.
DataTypes dst_array_types;
for (size_t i = 2; i < args.size() - 1; i += 2)
dst_array_types.push_back(args[i]);
// Type of the ELSE branch
dst_array_types.push_back(args.back());
return getLeastSupertype(dst_array_types);
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & args, const DataTypePtr & result_type, size_t input_rows_count) const override
{
if (args.empty())
throw Exception(ErrorCodes::TOO_FEW_ARGUMENTS_FOR_FUNCTION, "Function {} expects at least 1 argument", getName());
/// In the following code, we turn the construction:
/// CASE expr WHEN val[0] THEN branch[0] ... WHEN val[N-1] then branch[N-1] ELSE branchN
/// into the construction transform(expr, src, dest, branchN)
/// where:
/// src = [val[0], val[1], ..., val[N-1]]
/// dst = [branch[0], ..., branch[N-1]]
/// then we perform it.
/// Create the arrays required by the transform function.
ColumnsWithTypeAndName src_array_elems;
DataTypes src_array_types;
ColumnsWithTypeAndName dst_array_elems;
DataTypes dst_array_types;
for (size_t i = 1; i < (args.size() - 1); ++i)
{
if (i % 2)
{
src_array_elems.push_back(args[i]);
src_array_types.push_back(args[i].type);
}
else
{
dst_array_elems.push_back(args[i]);
dst_array_types.push_back(args[i].type);
}
}
DataTypePtr src_array_type = std::make_shared<DataTypeArray>(getLeastSupertype(src_array_types));
DataTypePtr dst_array_type = std::make_shared<DataTypeArray>(getLeastSupertype(dst_array_types));
ColumnWithTypeAndName src_array_col{nullptr, src_array_type, ""};
ColumnWithTypeAndName dst_array_col{nullptr, dst_array_type, ""};
auto fun_array = FunctionFactory::instance().get("array", context);
src_array_col.column = fun_array->build(src_array_elems)->execute(src_array_elems, src_array_type, input_rows_count);
dst_array_col.column = fun_array->build(dst_array_elems)->execute(dst_array_elems, dst_array_type, input_rows_count);
/// Execute transform.
ColumnsWithTypeAndName transform_args{args.front(), src_array_col, dst_array_col, args.back()};
return FunctionFactory::instance().get("transform", context)->build(transform_args)
->execute(transform_args, result_type, input_rows_count);
}
private:
ContextPtr context;
};
}
REGISTER_FUNCTION(CaseWithExpression)
{
factory.registerFunction<FunctionCaseWithExpression>();
/// These are obsolete function names.
factory.registerFunction<FunctionCaseWithExpression>("caseWithExpr");
}
}
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