{

JSONObjectWriter w(out, "ExplainQuery");

w.writeString("kind", toString(kind));

w.writeChild("settings", ast_settings);

w.writeChild("query", query);

w.writeChild("table_function", table_function);

w.writeChild("table_override", table_override);

writeOutputOptionsJSON(w);

{

JSONObjectReader r(json);

kind = fromString(r.getString("kind"));

/// `InterpreterExplainQuery` reads `settings` as an `ASTSetQuery`, the table function as an

/// `ASTFunction`, and the override as an `ASTTableOverride`; restore those with typed reads.

auto settings_child = r.readChildOfType<ASTSetQuery>("settings");

if (settings_child)

setSettings(std::move(settings_child));

auto query_child = r.readChild("query");

if (query_child)

setExplainedQuery(std::move(query_child));

auto table_function_child = r.readChildOfType<ASTFunction>("table_function");

if (table_function_child)

setTableFunction(std::move(table_function_child));

auto table_override_child = r.readChildOfType<ASTTableOverride>("table_override");

if (table_override_child)

setTableOverride(std::move(table_override_child));

/// Enforce the exact parser-produced child set per kind, rejecting forbidden extras as well:

/// `EXPLAIN TABLE OVERRIDE` dereferences the table function and override but never parses an

/// explained query, `EXPLAIN CURRENT TRANSACTION` explains nothing, and every other kind

/// dereferences the explained query (e.g. `dumpAST(*getExplainedQuery())`) and never parses a

/// table function or override. An extra child would format into parser-impossible SQL while

/// `InterpreterExplainQuery` silently ignores it.

switch (kind)

{

case ExplainKind::TableOverride:

if (!getTableFunction() || !getTableOverride())

throw Exception(ErrorCodes::BAD_ARGUMENTS,

"EXPLAIN TABLE OVERRIDE requires 'table_function' and 'table_override' during AST JSON deserialization");

if (getExplainedQuery())

throw Exception(ErrorCodes::BAD_ARGUMENTS,

"EXPLAIN TABLE OVERRIDE cannot carry an explained 'query' during AST JSON deserialization");

/// `ParserExplainQuery` parses the override with `ParserTableOverrideDeclaration(false)`,

/// so it is always the embedded form: not standalone and without a table name. A standalone

/// override would format as `EXPLAIN TABLE OVERRIDE <function> TABLE OVERRIDE name ...`,

/// which the SQL parser can never produce back.

{

const auto & override_ast = getTableOverride()->as<const ASTTableOverride &>();

if (override_ast.is_standalone || !override_ast.table_name.empty())

throw Exception(ErrorCodes::BAD_ARGUMENTS,

"EXPLAIN TABLE OVERRIDE requires an embedded table override (not standalone, without "

"'table_name') during AST JSON deserialization");

}

break;

case ExplainKind::CurrentTransaction:

if (getExplainedQuery() || getTableFunction() || getTableOverride())

throw Exception(ErrorCodes::BAD_ARGUMENTS,

"EXPLAIN CURRENT TRANSACTION cannot carry 'query', 'table_function', or 'table_override' during AST JSON deserialization");

break;

default:

if (!getExplainedQuery())

throw Exception(ErrorCodes::BAD_ARGUMENTS,

"{} requires an explained query during AST JSON deserialization", toString(kind));

if (getTableFunction() || getTableOverride())

throw Exception(ErrorCodes::BAD_ARGUMENTS,

"'table_function' and 'table_override' are only valid for EXPLAIN TABLE OVERRIDE during AST JSON deserialization");

break;

}

readOutputOptionsJSON(r);