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55 lines
1.2 KiB
C++
55 lines
1.2 KiB
C++
#pragma once
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#include <DB/Parsers/IAST.h>
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#include <unordered_map>
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namespace DB
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{
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class WriteBuffer;
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/** Build a map: alias -> AST node.
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*
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* Also fill information about what kind each alias has:
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* - expression alias;
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* - table alias;
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* - ARRAY JOIN alias.
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*
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* As extension to standard SQL, aliases could be specified and used in any part of query.
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* Example: SELECT a, (1 AS a) + 1 AS b FROM t GROUP BY a, b
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* Alias could be used in query before it is defined.
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*
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* Aliases could not be redefined. Example: 1 AS a, a + 1 AS a - is prohibited.
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*
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* Don't descend into subqueries (as aliases are local inside them).
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*/
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struct CollectAliases
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{
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void process(const ASTPtr & ast);
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enum class Kind
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{
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Expression, /// Example: SELECT a AS b, f(x) AS y
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Table, /// Example: SELECT t.* FROM (SELECT 1) AS t
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ArrayJoin /// Example: SELECT t.x.a FROM t ARRAY JOIN arr AS x
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};
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struct AliasInfo
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{
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ASTPtr node;
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Kind kind;
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AliasInfo(ASTPtr node, Kind kind) : node(node), kind(kind) {}
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};
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using Aliases = std::unordered_map<String, AliasInfo>;
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Aliases aliases;
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/// Debug output
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void dump(WriteBuffer & out) const;
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};
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}
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