Function exprTypmod

src/backend/nodes/nodeFuncs.c:287–510

* exprTypmod - * returns the type-specific modifier of the expression's result type, * if it can be determined. In many cases, it can't and we return -1. */

 *	  if it can be determined.  In many cases, it can't and we return -1.
 */
int32
exprTypmod(const Node *expr)
{
	if (!expr)
		return -1;

	switch (nodeTag(expr))
	{
		case T_Var:
			return ((const Var *) expr)->vartypmod;
		case T_Const:
			return ((const Const *) expr)->consttypmod;
		case T_Param:
			return ((const Param *) expr)->paramtypmod;
		case T_SubscriptingRef:
			return ((const SubscriptingRef *) expr)->reftypmod;
		case T_FuncExpr:
			{
				int32		coercedTypmod;

				/* Be smart about length-coercion functions... */
				if (exprIsLengthCoercion(expr, &coercedTypmod))
					return coercedTypmod;
			}
			break;
		case T_NamedArgExpr:
			return exprTypmod((Node *) ((const NamedArgExpr *) expr)->arg);
		case T_NullIfExpr:
			{
				/*
				 * Result is either first argument or NULL, so we can report
				 * first argument's typmod if known.
				 */
				const NullIfExpr *nexpr = (const NullIfExpr *) expr;

				return exprTypmod((Node *) linitial(nexpr->args));
			}
			break;
		case T_SubLink:
			{
				const SubLink *sublink = (const SubLink *) expr;

				if (sublink->subLinkType == EXPR_SUBLINK ||
					sublink->subLinkType == ARRAY_SUBLINK)
				{
					/* get the typmod of the subselect's first target column */
					Query	   *qtree = (Query *) sublink->subselect;
					TargetEntry *tent;

					if (!qtree || !IsA(qtree, Query))
						elog(ERROR, "cannot get type for untransformed sublink");
					tent = linitial_node(TargetEntry, qtree->targetList);
					Assert(!tent->resjunk);
					return exprTypmod((Node *) tent->expr);
					/* note we don't need to care if it's an array */
				}
				/* otherwise, result is RECORD or BOOLEAN, typmod is -1 */
			}