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/Parsers/ASTIdentifier.h>
#include <DB/Interpreters/Context.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>
namespace DB
{
/** Вернуть названия и типы столбцов указанной таблицы.
*/
class InterpreterDescribeQuery
{
public:
InterpreterDescribeQuery(ASTPtr query_ptr_, Context & context_)
: query_ptr(query_ptr_), context(context_) {}
BlockIO execute()
{
BlockIO res;
res.in = executeImpl();
res.in_sample = getSampleBlock();
return res;
}
BlockInputStreamPtr executeAndFormat(WriteBuffer & buf)
{
Block sample = getSampleBlock();
ASTPtr format_ast = dynamic_cast<ASTDescribeQuery &>(*query_ptr).format;
String format_name = format_ast ? dynamic_cast<ASTIdentifier &>(*format_ast).name : context.getDefaultFormat();
BlockInputStreamPtr in = executeImpl();
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BlockOutputStreamPtr out = context.getFormatFactory().getOutput(format_name, buf, sample);
copyData(*in, *out);
return in;
}
private:
ASTPtr query_ptr;
Context context;
Block getSampleBlock()
{
Block block;
ColumnWithNameAndType col;
col.name = "name";
col.type = new DataTypeString;
col.column = col.type->createColumn();
block.insert(col);
col.name = "type";
block.insert(col);
return block;
}
BlockInputStreamPtr executeImpl()
{
const ASTDescribeQuery & ast = dynamic_cast<const ASTDescribeQuery &>(*query_ptr);
NamesAndTypesList columns;
{
StoragePtr table = context.getTable(ast.database, ast.table);
auto table_lock = table->lockStructure(false);
columns = table->getColumnsList();
}
ColumnString * name_column = new ColumnString;
ColumnString * type_column = new ColumnString;
Block block;
block.insert(ColumnWithNameAndType(name_column, new DataTypeString, "name"));
block.insert(ColumnWithNameAndType(type_column, new DataTypeString, "type"));
for (NamesAndTypesList::iterator it = columns.begin(); it != columns.end(); ++it)
{
name_column->insert(it->first);
type_column->insert(it->second->getName());
}
return new OneBlockInputStream(block);
}
};
}