Function applyRelabelType

src/backend/nodes/nodeFuncs.c:602–647

* applyRelabelType * Add a RelabelType node if needed to make the expression expose * the specified type, typmod, and collation. * * This is primarily intended to be used during planning. Therefore, it must * maintain the post-eval_const_expressions invariants that there are not * adjacent RelabelTypes, and that the tree is fully const-folded (hence, * we mustn't return a RelabelType ato

 * passed as true if caller knows the Const is newly generated.
 */
Node *
applyRelabelType(Node *arg, Oid rtype, int32 rtypmod, Oid rcollid,
				 CoercionForm rformat, int rlocation, bool overwrite_ok)
{
	/*
	 * If we find stacked RelabelTypes (eg, from foo::int::oid) we can discard
	 * all but the top one, and must do so to ensure that semantically
	 * equivalent expressions are equal().
	 */
	while (arg && IsA(arg, RelabelType))
		arg = (Node *) ((RelabelType *) arg)->arg;

	if (arg && IsA(arg, Const))
	{
		/* Modify the Const directly to preserve const-flatness. */
		Const	   *con = (Const *) arg;

		if (!overwrite_ok)
			con = copyObject(con);
		con->consttype = rtype;
		con->consttypmod = rtypmod;
		con->constcollid = rcollid;
		/* We keep the Const's original location. */
		return (Node *) con;
	}
	else if (exprType(arg) == rtype &&
			 exprTypmod(arg) == rtypmod &&
			 exprCollation(arg) == rcollid)
	{
		/* Sometimes we find a nest of relabels that net out to nothing. */
		return arg;
	}
	else
	{
		/* Nope, gotta have a RelabelType. */
		RelabelType *newrelabel = makeNode(RelabelType);

		newrelabel->arg = (Expr *) arg;
		newrelabel->resulttype = rtype;
		newrelabel->resulttypmod = rtypmod;
		newrelabel->resultcollid = rcollid;
		newrelabel->relabelformat = rformat;
		newrelabel->location = rlocation;
		return (Node *) newrelabel;
	}
}

/*
 * relabel_to_typmod