ClickHouse/dbms/Interpreters/evaluateConstantExpression.h

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