ClickHouse/dbms/src/Functions/caseWithExpression.cpp

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#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypeArray.h>
#include <DataTypes/getLeastSupertype.h>
#include <ext/map.h>
namespace DB
{
namespace ErrorCodes
{
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extern const int TOO_FEW_ARGUMENTS_FOR_FUNCTION;
}
/// 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(const Context & context_) { return std::make_shared<FunctionCaseWithExpression>(context_); }
public:
FunctionCaseWithExpression(const Context & context_) : context(context_) {}
bool isVariadic() const override { return true; }
size_t getNumberOfArguments() const override { return 0; }
String getName() const override { return name; }
DataTypePtr getReturnTypeImpl(const DataTypes & args) const override
{
if (!args.size())
throw Exception{"Function " + getName() + " expects at least 1 arguments",
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ErrorCodes::TOO_FEW_ARGUMENTS_FOR_FUNCTION};
/// 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]);
return getLeastSupertype(dst_array_types);
}
void executeImpl(Block & block, const ColumnNumbers & args, size_t result, size_t input_rows_count) override
{
if (!args.size())
throw Exception{"Function " + getName() + " expects at least 1 argument",
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ErrorCodes::TOO_FEW_ARGUMENTS_FOR_FUNCTION};
/// 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.
ColumnNumbers src_array_args;
ColumnsWithTypeAndName src_array_elems;
DataTypes src_array_types;
ColumnNumbers dst_array_args;
ColumnsWithTypeAndName dst_array_elems;
DataTypes dst_array_types;
for (size_t i = 1; i < (args.size() - 1); ++i)
{
if (i % 2)
{
src_array_args.push_back(args[i]);
src_array_elems.push_back(block.getByPosition(args[i]));
src_array_types.push_back(block.getByPosition(args[i]).type);
}
else
{
dst_array_args.push_back(args[i]);
dst_array_elems.push_back(block.getByPosition(args[i]));
dst_array_types.push_back(block.getByPosition(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));
Block temp_block = block;
size_t src_array_pos = temp_block.columns();
temp_block.insert({nullptr, src_array_type, ""});
size_t dst_array_pos = temp_block.columns();
temp_block.insert({nullptr, dst_array_type, ""});
auto fun_array = FunctionFactory::instance().get("array", context);
fun_array->build(src_array_elems)->execute(temp_block, src_array_args, src_array_pos, input_rows_count);
fun_array->build(dst_array_elems)->execute(temp_block, dst_array_args, dst_array_pos, input_rows_count);
/// Execute transform.
ColumnNumbers transform_args{args.front(), src_array_pos, dst_array_pos, args.back()};
FunctionFactory::instance().get("transform", context)->build(
ext::map<ColumnsWithTypeAndName>(transform_args, [&](auto i){ return temp_block.getByPosition(i); }))
->execute(temp_block, transform_args, result, input_rows_count);
/// Put the result into the original block.
block.getByPosition(result).column = std::move(temp_block.getByPosition(result).column);
}
private:
const Context & context;
};
void registerFunctionCaseWithExpression(FunctionFactory & factory)
{
factory.registerFunction<FunctionCaseWithExpression>();
/// These are obsolete function names.
factory.registerFunction<FunctionCaseWithExpression>("caseWithExpr");
}
}