ClickHouse/dbms/src/Dictionaries/ExternalQueryBuilder.h

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#pragma once
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#include <string>
#include <Columns/IColumn.h>
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namespace DB
{
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struct DictionaryStructure;
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class WriteBuffer;
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/** Builds a query to load data from external database.
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*/
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(
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const Columns & key_columns,
const std::vector<size_t> & requested_rows,
LoadKeysMethod method);
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private:
/// Expression in form (x = c1 AND y = c2 ...)
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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, ...)
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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;
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};
}