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#include <Parsers/ExpressionListParsers.h>
#include <Parsers/ParserSelectWithUnionQuery.h>
#include <Parsers/ASTSelectWithUnionQuery.h>
#include <Parsers/ParserUnionQueryElement.h>
#include <Parsers/ASTExpressionList.h>
namespace DB
{
bool ParserSelectWithUnionQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
ASTPtr list_node;
ParserUnionList parser;
if (!parser.parse(pos, list_node, expected))
return false;
/// NOTE: We can't simply flatten inner union query now, since we may have different union mode in query,
/// so flatten may change it's semantics. For example:
/// flatten `SELECT 1 UNION (SELECT 1 UNION ALL SELECT 1)` -> `SELECT 1 UNION SELECT 1 UNION ALL SELECT 1`
/// If we got only one child which is ASTSelectWithUnionQuery, just lift it up
auto & expr_list = list_node->as<ASTExpressionList &>();
if (expr_list.children.size() == 1)
{
if (expr_list.children.at(0)->as<ASTSelectWithUnionQuery>())
{
node = std::move(expr_list.children.at(0));
return true;
}
}
auto select_with_union_query = std::make_shared<ASTSelectWithUnionQuery>();
node = select_with_union_query;
select_with_union_query->list_of_selects = list_node;
select_with_union_query->children.push_back(select_with_union_query->list_of_selects);
select_with_union_query->list_of_modes = parser.getUnionModes();
return true;
}
}
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