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Better UNION ALL: development #1947

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This commit is contained in:
Alexey Milovidov 2018-02-27 23:43:42 +03:00
parent a3386b3eba
commit 492053bc43
1 changed files with 26 additions and 41 deletions
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67
dbms/src/Interpreters/InterpreterSelectWithUnionQuery.cpp
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@ -38,63 +38,48 @@ InterpreterSelectWithUnionQuery::InterpreterSelectWithUnionQuery(
if (!num_selects)
throw Exception("Logical error: no children in ASTSelectWithUnionQuery", ErrorCodes::LOGICAL_ERROR);
/// Check number of columns.
size_t num_columns = 0;
for (const auto & select : ast.list_of_selects->children)
{
size_t current_num_columns = typeid_cast<const ASTSelectQuery &>(*select).select_expression_list->children.size();
if (!current_num_columns)
throw Exception("Logical error: SELECT query has zero columns in SELECT clause", ErrorCodes::LOGICAL_ERROR);
if (!num_columns)
num_columns = current_num_columns;
else if (num_columns != current_num_columns)
throw Exception("Different number of columns in UNION ALL elements.", ErrorCodes::UNION_ALL_RESULT_STRUCTURES_MISMATCH);
}
/// Initialize interpreters for each SELECT query.
/// Note that we pass 'required_result_column_names' to first SELECT.
/// And for the rest, we pass names at the corresponding positions of 'required_result_column_names' of the first SELECT,
/// And for the rest, we pass names at the corresponding positions of 'required_result_column_names' in the result of first SELECT,
/// because names could be different.
nested_interpreters.reserve(num_selects);
std::vector<size_t> positions_of_required_result_columns(required_result_column_names.size());
std::vector<Names> required_result_column_names_for_other_selects(num_selects);
if (!required_result_column_names.empty())
{
const auto & first_select = static_cast<const ASTSelectQuery &>(*ast.list_of_selects->children.at(0));
/// Result header if there are no filtering by 'required_result_column_names'.
/// We use it to determine positions of 'required_result_column_names' in SELECT clause.
Block full_result_header = InterpreterSelectQuery(
ast.list_of_selects->children.at(0), context, Names(), to_stage, subquery_depth).getSampleBlock();
std::vector<size_t> positions_of_required_result_columns(required_result_column_names.size());
for (size_t required_result_num = 0, size = required_result_column_names.size(); required_result_num < size; ++required_result_num)
positions_of_required_result_columns[required_result_num] = full_result_header.getPositionByName(required_result_column_names[required_result_num]);
for (size_t query_num = 1; query_num < num_selects; ++query_num)
{
bool found = false;
for (size_t position_in_select = 0; position_in_select < num_columns; ++position_in_select)
{
if (first_select.select_expression_list->children.at(position_in_select)->getAliasOrColumnName()
== required_result_column_names[required_result_num])
{
found = true;
positions_of_required_result_columns[required_result_num] = position_in_select;
break;
}
}
if (!found)
throw Exception("Logical error: cannot find result column " + backQuoteIfNeed(required_result_column_names[required_result_num])
+ " in first SELECT query in UNION ALL", ErrorCodes::LOGICAL_ERROR);
Block full_result_header_for_current_select = InterpreterSelectQuery(
ast.list_of_selects->children.at(query_num), context, Names(), to_stage, subquery_depth).getSampleBlock();
if (full_result_header_for_current_select.columns() != full_result_header.columns())
throw Exception("Different number of columns in UNION ALL elements", ErrorCodes::UNION_ALL_RESULT_STRUCTURES_MISMATCH);
required_result_column_names_for_other_selects[query_num].reserve(required_result_column_names.size());
for (const auto & pos : positions_of_required_result_columns)
required_result_column_names_for_other_selects[query_num].push_back(full_result_header_for_current_select.getByPosition(pos).name);
}
}
for (size_t query_num = 0; query_num < num_selects; ++query_num)
{
const auto & select = ast.list_of_selects->children.at(query_num);
Names current_required_result_column_names(required_result_column_names.size());
for (size_t required_result_num = 0, size = required_result_column_names.size(); required_result_num < size; ++required_result_num)
current_required_result_column_names[required_result_num]
= static_cast<const ASTSelectQuery &>(*select).select_expression_list
->children.at(positions_of_required_result_columns[required_result_num])->getAliasOrColumnName();
const Names & current_required_result_column_names = query_num == 0
? required_result_column_names
: required_result_column_names_for_other_selects[query_num];
nested_interpreters.emplace_back(std::make_unique<InterpreterSelectQuery>(select, context, current_required_result_column_names, to_stage, subquery_depth));
nested_interpreters.emplace_back(std::make_unique<InterpreterSelectQuery>(
ast.list_of_selects->children.at(query_num), context, current_required_result_column_names, to_stage, subquery_depth));
}
/// Determine structure of result.