ClickHouse/dbms/src/Dictionaries/ExternalQueryBuilder.h
2017-05-25 22:52:05 +03:00

80 lines
2.2 KiB
C++

#pragma once
#include <string>
#include <Columns/IColumn.h>
namespace DB
{
struct DictionaryStructure;
class WriteBuffer;
/** Builds a query to load data from external database.
*/
struct ExternalQueryBuilder
{
const DictionaryStructure & dict_struct;
const std::string & db;
const std::string & table;
const std::string & where;
/// Method to quote identifiers.
/// NOTE There could be differences in escaping rules inside quotes. Escaping rules may not match that required by specific external DBMS.
enum QuotingStyle
{
None, /// Write as-is, without quotes.
Backticks, /// `mysql` style
DoubleQuotes /// "postgres" style
};
QuotingStyle quoting_style;
ExternalQueryBuilder(
const DictionaryStructure & dict_struct,
const std::string & db,
const std::string & table,
const std::string & where,
QuotingStyle quoting_style);
/** Generate a query to load all data. */
std::string composeLoadAllQuery() const;
/** Generate a query to load data by set of UInt64 keys. */
std::string composeLoadIdsQuery(const std::vector<UInt64> & ids);
/** Generate a query to load data by set of composite keys.
* There are two methods of specification of composite keys in WHERE:
* 1. (x = c11 AND y = c12) OR (x = c21 AND y = c22) ...
* 2. (x, y) IN ((c11, c12), (c21, c22), ...)
*/
enum LoadKeysMethod
{
AND_OR_CHAIN,
IN_WITH_TUPLES,
};
std::string composeLoadKeysQuery(
const Columns & key_columns,
const std::vector<size_t> & requested_rows,
LoadKeysMethod method);
private:
/// Expression in form (x = c1 AND y = c2 ...)
void composeKeyCondition(const Columns & key_columns, const size_t row, WriteBuffer & out) const;
/// Expression in form (x, y, ...)
std::string composeKeyTupleDefinition() const;
/// Expression in form (c1, c2, ...)
void composeKeyTuple(const Columns & key_columns, const size_t row, WriteBuffer & out) const;
/// Write string with specified quoting style.
void writeQuoted(const std::string & s, WriteBuffer & out) const;
};
}