ClickHouse/dbms/include/DB/Interpreters/evaluateMissingDefaults.h

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#pragma once
#include <DB/Core/Block.h>
#include <DB/Storages/ColumnDefault.h>
#include <DB/Interpreters/ExpressionAnalyzer.h>
#include <utility>
namespace DB
{
inline void evaluateMissingDefaults(Block & block,
const NamesAndTypesList & required_columns,
const ColumnDefaults & column_defaults,
const Context & context)
{
if (column_defaults.empty())
return;
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ASTPtr default_expr_list{std::make_unique<ASTExpressionList>().release()};
for (const auto & column : required_columns)
{
if (block.has(column.name))
continue;
const auto it = column_defaults.find(column.name);
/// expressions must be cloned to prevent modification by the ExpressionAnalyzer
if (it != column_defaults.end())
default_expr_list->children.emplace_back(
setAlias(it->second.expression->clone(), it->first));
}
/// nothing to evaluate
if (default_expr_list->children.empty())
return;
/** ExpressionAnalyzer eliminates "unused" columns, in order to ensure their safety
* we are going to operate on a copy instead of the original block */
Block copy_block{block};
/// evaluate default values for defaulted columns
ExpressionAnalyzer{default_expr_list, context, required_columns}.getActions(true)->execute(copy_block);
/// move evaluated columns to the original block
for (auto & column_name_type : copy_block.getColumns())
block.insert(std::move(column_name_type));
}
}