Function transformSetOperationTree_internal

src/backend/parser/analyze.c:2241–2472

static Node *
transformSetOperationTree_internal(ParseState *pstate, SelectStmt *stmt,
								   bool isTopLevel, setop_types_ctx *setop_types)
{
	bool		isLeaf;

	Assert(stmt && IsA(stmt, SelectStmt));

	/* Guard against stack overflow due to overly complex set-expressions */
	check_stack_depth();

	/*
	 * Validity-check both leaf and internal SELECTs for disallowed ops.
	 */
	if (stmt->intoClause)
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR),
				 errmsg("INTO is only allowed on first SELECT of UNION/INTERSECT/EXCEPT"),
				 parser_errposition(pstate,
									exprLocation((Node *) stmt->intoClause))));

	/* We don't support FOR UPDATE/SHARE with set ops at the moment. */
	if (stmt->lockingClause)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
		/*------
		  translator: %s is a SQL row locking clause such as FOR UPDATE */
				 errmsg("%s is not allowed with UNION/INTERSECT/EXCEPT",
						LCS_asString(((LockingClause *)
									  linitial(stmt->lockingClause))->strength))));

	/*
	 * If an internal node of a set-op tree has ORDER BY, LIMIT, FOR UPDATE,
	 * or WITH clauses attached, we need to treat it like a leaf node to
	 * generate an independent sub-Query tree.  Otherwise, it can be
	 * represented by a SetOperationStmt node underneath the parent Query.
	 */
	if (stmt->op == SETOP_NONE)
	{
		Assert(stmt->larg == NULL && stmt->rarg == NULL);
		isLeaf = true;
	}
	else
	{
		Assert(stmt->larg != NULL && stmt->rarg != NULL);
		if (stmt->sortClause || stmt->limitOffset || stmt->limitCount ||
			stmt->lockingClause || stmt->withClause)
			isLeaf = true;
		else
			isLeaf = false;
	}

	if (isLeaf)
	{
		/* Process leaf SELECT */
		Query	   *selectQuery;
		char		selectName[32];
		ParseNamespaceItem *nsitem;