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112 lines
3.7 KiB
C++
112 lines
3.7 KiB
C++
#include <Common/typeid_cast.h>
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#include <Parsers/ASTLiteral.h>
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#include <Parsers/ASTFunction.h>
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#include <Parsers/ASTExpressionList.h>
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#include <Interpreters/OptimizeIfWithConstantConditionVisitor.h>
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#include <IO/WriteHelpers.h>
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namespace DB
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{
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namespace ErrorCodes
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{
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extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
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}
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static bool tryExtractConstValueFromCondition(const ASTPtr & condition, bool & value)
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{
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/// numeric constant in condition
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if (const auto * literal = condition->as<ASTLiteral>())
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{
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if (literal->value.getType() == Field::Types::Int64 ||
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literal->value.getType() == Field::Types::UInt64)
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{
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value = literal->value.get<Int64>();
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return true;
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}
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}
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/// cast of numeric constant in condition to UInt8
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if (const auto * function = condition->as<ASTFunction>())
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{
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if (function->name == "CAST")
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{
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if (const auto * expr_list = function->arguments->as<ASTExpressionList>())
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{
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if (expr_list->children.size() != 2)
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throw Exception("Function CAST must have exactly two arguments", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
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const ASTPtr & type_ast = expr_list->children.at(1);
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if (const auto * type_literal = type_ast->as<ASTLiteral>())
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{
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if (type_literal->value.getType() == Field::Types::String &&
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type_literal->value.get<std::string>() == "UInt8")
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return tryExtractConstValueFromCondition(expr_list->children.at(0), value);
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}
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}
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}
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}
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return false;
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}
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void OptimizeIfWithConstantConditionVisitor::visit(ASTPtr & current_ast)
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{
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if (!current_ast)
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return;
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for (ASTPtr & child : current_ast->children)
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{
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auto * function_node = child->as<ASTFunction>();
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if (!function_node || function_node->name != "if")
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{
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visit(child);
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continue;
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}
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visit(function_node->arguments);
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const auto * args = function_node->arguments->as<ASTExpressionList>();
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if (args->children.size() != 3)
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throw Exception("Wrong number of arguments for function 'if' (" + toString(args->children.size()) + " instead of 3)",
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ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
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ASTPtr condition_expr = args->children[0];
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ASTPtr then_expr = args->children[1];
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ASTPtr else_expr = args->children[2];
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bool condition;
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if (tryExtractConstValueFromCondition(condition_expr, condition))
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{
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ASTPtr replace_ast = condition ? then_expr : else_expr;
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ASTPtr child_copy = child;
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String replace_alias = replace_ast->tryGetAlias();
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String if_alias = child->tryGetAlias();
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if (replace_alias.empty())
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{
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replace_ast->setAlias(if_alias);
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child = replace_ast;
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}
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else
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{
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/// Only copy of one node is required here.
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/// But IAST has only method for deep copy of subtree.
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/// This can be a reason of performance degradation in case of deep queries.
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ASTPtr replace_ast_deep_copy = replace_ast->clone();
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replace_ast_deep_copy->setAlias(if_alias);
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child = replace_ast_deep_copy;
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}
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if (!if_alias.empty())
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{
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auto alias_it = aliases.find(if_alias);
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if (alias_it != aliases.end() && alias_it->second.get() == child_copy.get())
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alias_it->second = child;
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}
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}
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}
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}
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}
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