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47 lines
1.4 KiB
C++
47 lines
1.4 KiB
C++
#pragma once
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#include <ext/shared_ptr_helper.h>
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#include <Storages/IStorage.h>
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namespace DB
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{
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class Context;
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/** Implements a table engine for the system table "numbers".
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* The table contains the only column number UInt64.
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* From this table, you can read all natural numbers, starting from 0 (to 2^64 - 1, and then again).
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*
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* You could also specify a limit (how many numbers to give).
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* If multithreaded is specified, numbers will be generated in several streams
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* (and result could be out of order). If both multithreaded and limit are specified,
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* the table could give you not exactly 1..limit range, but some arbitary 'limit' numbers.
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*/
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class StorageSystemNumbers : public ext::shared_ptr_helper<StorageSystemNumbers>, public IStorage
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{
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public:
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std::string getName() const override { return "SystemNumbers"; }
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std::string getTableName() const override { return name; }
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BlockInputStreams read(
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const Names & column_names,
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const SelectQueryInfo & query_info,
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const Context & context,
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QueryProcessingStage::Enum & processed_stage,
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size_t max_block_size,
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unsigned num_streams) override;
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private:
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const std::string name;
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bool multithreaded;
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size_t limit;
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protected:
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/// limit: 0 means unlimited.
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StorageSystemNumbers(const std::string & name_, bool multithreaded_, size_t limit_ = 0);
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};
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}
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