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56 lines
2.0 KiB
C++
56 lines
2.0 KiB
C++
#pragma once
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#include <Core/Block.h>
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#include <Core/Field.h>
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#include <Interpreters/Context_fwd.h>
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#include <Parsers/IAST.h>
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#include <memory>
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#include <optional>
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namespace DB
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{
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class ExpressionActions;
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class IDataType;
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using ExpressionActionsPtr = std::shared_ptr<ExpressionActions>;
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/** Evaluate constant expression and its type.
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* Used in rare cases - for elements of set for IN, for data to INSERT.
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* Throws exception if it's not a constant expression.
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* Quite suboptimal.
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*/
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std::pair<Field, std::shared_ptr<const IDataType>> evaluateConstantExpression(const ASTPtr & node, ContextPtr context);
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/** Evaluate constant expression and returns ASTLiteral with its value.
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*/
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ASTPtr evaluateConstantExpressionAsLiteral(const ASTPtr & node, ContextPtr context);
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/** Evaluate constant expression and returns ASTLiteral with its value.
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* Also, if AST is identifier, then return string literal with its name.
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* Useful in places where some name may be specified as identifier, or as result of a constant expression.
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*/
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ASTPtr evaluateConstantExpressionOrIdentifierAsLiteral(const ASTPtr & node, ContextPtr context);
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/** The same as evaluateConstantExpressionOrIdentifierAsLiteral(...),
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* but if result is an empty string, replace it with current database name
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* or default database name.
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*/
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ASTPtr evaluateConstantExpressionForDatabaseName(const ASTPtr & node, ContextPtr context);
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/** Try to fold condition to countable set of constant values.
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* @param node a condition that we try to fold.
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* @param target_expr expression evaluated over a set of constants.
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* @param limit limit for number of values
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* @return optional blocks each with a single row and a single column for target expression,
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* or empty blocks if condition is always false,
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* or nothing if condition can't be folded to a set of constants.
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*/
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std::optional<Blocks> evaluateExpressionOverConstantCondition(const ASTPtr & node, const ExpressionActionsPtr & target_expr, size_t & limit);
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}
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