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#pragma once
#include <Interpreters/InDepthNodeVisitor.h>
#include <Interpreters/DatabaseAndTableWithAlias.h>
#include <Interpreters/Aliases.h>
namespace DB
{
class ASTSelectQuery;
class Context;
/// AST transformer. It replaces multiple joins to (subselect + join) track.
/// 'select * from t1 join t2 on ... join t3 on ... join t4 on ...' would be rewritten with
/// 'select * from (select * from t1 join t2 on ...) join t3 on ...) join t4 on ...'
class JoinToSubqueryTransformMatcher
{
public:
struct Data
{
const std::vector<TableWithColumnNamesAndTypes> & tables;
const Aliases & aliases;
bool done = false;
bool try_to_keep_original_names = false;
};
static bool needChildVisit(ASTPtr &, const ASTPtr &);
static void visit(ASTPtr & ast, Data & data);
private:
/// - combines two source TablesInSelectQueryElement into resulting one (Subquery)
/// - adds table hidings to ASTSelectQuery.with_expression_list
///
/// TablesInSelectQueryElement [result]
/// TableExpression
/// Subquery (alias __join1)
/// SelectWithUnionQuery
/// ExpressionList
/// SelectQuery
/// ExpressionList
/// Asterisk
/// TablesInSelectQuery
/// TablesInSelectQueryElement [source1]
/// TablesInSelectQueryElement [source2]
///
static void visit(ASTSelectQuery & select, ASTPtr & ast, Data & data);
/// @return combined TablesInSelectQueryElement or nullptr if cannot rewrite
static ASTPtr replaceJoin(ASTPtr left, ASTPtr right, ASTPtr subquery_template);
};
using JoinToSubqueryTransformVisitor = InDepthNodeVisitor<JoinToSubqueryTransformMatcher, true>;
}
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