ClickHouse/dbms/src/Parsers/ASTWithAlias.cpp

#include <Parsers/ASTWithAlias.h>
#include <IO/WriteBufferFromOStream.h>
#include <IO/WriteHelpers.h>


namespace DB
{

void ASTWithAlias::formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const
{
    if (!alias.empty())
    {
        /// If we have previously output this node elsewhere in the query, now it is enough to output only the alias.
        if (!state.printed_asts_with_alias.emplace(frame.current_select, alias).second)
        {
            WriteBufferFromOStream wb(settings.ostr, 32);
            writeProbablyBackQuotedString(alias, wb);
            return;
        }
    }

    /// If there is an alias, then parentheses are required around the entire expression, including the alias. Because a record of the form `0 AS x + 0` is syntactically invalid.
    if (frame.need_parens && !alias.empty())
        settings.ostr <<'(';

    formatImplWithoutAlias(settings, state, frame);

    if (!alias.empty())
    {
        writeAlias(alias, settings.ostr, settings.hilite);
        if (frame.need_parens)
            settings.ostr <<')';
    }
}

}