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