1 | #pragma once |
2 | |
3 | #include <Parsers/IAST.h> |
4 | |
5 | |
6 | namespace DB |
7 | { |
8 | |
9 | |
10 | /** Base class for AST, which can contain an alias (identifiers, literals, functions). |
11 | */ |
12 | class ASTWithAlias : public IAST |
13 | { |
14 | public: |
15 | /// The alias, if any, or an empty string. |
16 | String alias; |
17 | /// If is true, getColumnName returns alias. Uses for aliases in former WITH section of SELECT query. |
18 | /// Example: 'WITH pow(2, 2) as a SELECT pow(a, 2)' returns 'pow(a, 2)' instead of 'pow(pow(2, 2), 2)' |
19 | bool prefer_alias_to_column_name = false; |
20 | |
21 | using IAST::IAST; |
22 | |
23 | void appendColumnName(WriteBuffer & ostr) const final; |
24 | String getAliasOrColumnName() const override { return alias.empty() ? getColumnName() : alias; } |
25 | String tryGetAlias() const override { return alias; } |
26 | void setAlias(const String & to) override { alias = to; } |
27 | |
28 | /// Calls formatImplWithoutAlias, and also outputs an alias. If necessary, encloses the entire expression in brackets. |
29 | void formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const override final; |
30 | |
31 | virtual void formatImplWithoutAlias(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const = 0; |
32 | |
33 | protected: |
34 | virtual void appendColumnNameImpl(WriteBuffer & ostr) const = 0; |
35 | |
36 | void writeAlias(const String & name, const FormatSettings & settings) const; |
37 | }; |
38 | |
39 | /// helper for setting aliases and chaining result to other functions |
40 | inline ASTPtr setAlias(ASTPtr ast, const String & alias) |
41 | { |
42 | ast->setAlias(alias); |
43 | return ast; |
44 | } |
45 | |
46 | |
47 | } |
48 | |