MySQL  8.0.27
Source Code Documentation
select_lex_visitor.h
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1 #ifndef Query_block_VISITOR_INCLUDED
2 #define Query_block_VISITOR_INCLUDED
3 /* Copyright (c) 2015, 2021, Oracle and/or its affiliates.
4 
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16  This program is distributed in the hope that it will be useful,
17  but WITHOUT ANY WARRANTY; without even the implied warranty of
18  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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24 
25 /**
26  @file select_lex_visitor.h
27  Visitor interface for parse trees.
28 */
29 
30 class Query_expression;
31 class Query_block;
32 class Item;
33 
34 /**
35  Abstract base class for traversing the Query_block tree. In order to use it,
36  a client defines a subclass, overriding the member functions that visit the
37  objects of interest. If a function returns true, traversal is aborted.
38 */
40  public:
41  virtual bool visits_in_prefix_order() const { return true; }
42 
43  bool visit(Query_expression *unit) { return visit_union(unit); }
44  bool visit(Query_block *query_block) {
45  return visit_query_block(query_block);
46  }
47 
48  /// Called for all nodes of all expression trees (i.e. Item trees).
49  bool visit(Item *item) { return visit_item(item); }
50 
51  virtual ~Select_lex_visitor() = 0;
52 
53  protected:
54  virtual bool visit_union(Query_expression *) { return false; }
55  virtual bool visit_query_block(Query_block *) { return false; }
56  virtual bool visit_item(Item *) { return false; }
57 };
58 
59 #endif // Query_block_VISITOR_INCLUDED
Base class that is used to represent any kind of expression in a relational query.
Definition: item.h:802
This class represents a query block, aka a query specification, which is a query consisting of a SELE...
Definition: sql_lex.h:1123
This class represents a query expression (one query block or several query blocks combined with UNION...
Definition: sql_lex.h:629
Abstract base class for traversing the Query_block tree.
Definition: select_lex_visitor.h:39
virtual bool visit_union(Query_expression *)
Definition: select_lex_visitor.h:54
virtual bool visit_item(Item *)
Definition: select_lex_visitor.h:56
bool visit(Query_expression *unit)
Definition: select_lex_visitor.h:43
virtual bool visit_query_block(Query_block *)
Definition: select_lex_visitor.h:55
bool visit(Item *item)
Called for all nodes of all expression trees (i.e. Item trees).
Definition: select_lex_visitor.h:49
virtual ~Select_lex_visitor()=0
Gcc demands an implementation for a virtual destructor.
virtual bool visits_in_prefix_order() const
Definition: select_lex_visitor.h:41
bool visit(Query_block *query_block)
Definition: select_lex_visitor.h:44