ClickHouse/dbms/include/DB/Interpreters/InterpreterDescribeQuery.h

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#pragma once
#include <DB/Storages/IStorage.h>
#include <DB/Parsers/TablePropertiesQueriesASTs.h>
#include <DB/Interpreters/Context.h>
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#include <DB/Interpreters/IInterpreter.h>
#include <DB/DataStreams/OneBlockInputStream.h>
#include <DB/DataStreams/BlockIO.h>
#include <DB/DataStreams/copyData.h>
#include <DB/DataTypes/DataTypesNumberFixed.h>
#include <DB/DataTypes/DataTypeString.h>
#include <DB/Columns/ColumnString.h>
#include <DB/Parsers/formatAST.h>
namespace DB
{
/** Вернуть названия и типы столбцов указанной таблицы.
*/
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class InterpreterDescribeQuery : public IInterpreter
{
public:
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InterpreterDescribeQuery(ASTPtr query_ptr_, const Context & context_)
: query_ptr(query_ptr_), context(context_) {}
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BlockIO execute() override
{
BlockIO res;
res.in = executeImpl();
res.in_sample = getSampleBlock();
return res;
}
private:
ASTPtr query_ptr;
Context context;
Block getSampleBlock()
{
Block block;
ColumnWithTypeAndName col;
col.name = "name";
col.type = new DataTypeString;
col.column = col.type->createColumn();
block.insert(col);
col.name = "type";
block.insert(col);
col.name = "default_type";
block.insert(col);
col.name = "default_expression";
block.insert(col);
return block;
}
BlockInputStreamPtr executeImpl()
{
const ASTDescribeQuery & ast = typeid_cast<const ASTDescribeQuery &>(*query_ptr);
NamesAndTypesList columns;
ColumnDefaults column_defaults;
{
StoragePtr table = context.getTable(ast.database, ast.table);
auto table_lock = table->lockStructure(false);
columns = table->getColumnsList();
columns.insert(std::end(columns), std::begin(table->alias_columns), std::end(table->alias_columns));
column_defaults = table->column_defaults;
}
ColumnWithTypeAndName name_column{std::make_shared<ColumnString>(), new DataTypeString, "name"};
ColumnWithTypeAndName type_column{std::make_shared<ColumnString>(), new DataTypeString, "type" };
ColumnWithTypeAndName default_type_column{std::make_shared<ColumnString>(), new DataTypeString, "default_type" };
ColumnWithTypeAndName default_expression_column{std::make_shared<ColumnString>(), new DataTypeString, "default_expression" };;
for (const auto column : columns)
{
name_column.column->insert(column.name);
type_column.column->insert(column.type->getName());
const auto it = column_defaults.find(column.name);
if (it == std::end(column_defaults))
{
default_type_column.column->insertDefault();
default_expression_column.column->insertDefault();
}
else
{
default_type_column.column->insert(toString(it->second.type));
default_expression_column.column->insert(queryToString(it->second.expression));
}
}
return new OneBlockInputStream{
{name_column, type_column, default_type_column, default_expression_column}
};
}
};
}