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#pragma once
#include <Analyzer/IQueryTreePass.h>
namespace DB
{
/** Optimize single `countDistinct` into `count` over subquery.
*
* Example: SELECT countDistinct(column) FROM table;
* Result: SELECT count() FROM (SELECT column FROM table GROUP BY column);
*/
class CountDistinctPass final : public IQueryTreePass
{
public:
String getName() override { return "CountDistinct"; }
String getDescription() override
{
return "Optimize single countDistinct into count over subquery";
}
void run(QueryTreeNodePtr query_tree_node, ContextPtr context) override;
};
}
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