mysql_num_rows() returns the
number of rows in a result set. This command is only valid
for SELECT statements. To retrieve the number of rows
affected by a INSERT, UPDATE or DELETE query, use
mysql_affected_rows().
注: If you use mysql_unbuffered_query(), mysql_num_rows() will not return the correct value until all the rows in the result set have been retrieved.
See also: mysql_affected_rows(),
mysql_connect(),
mysql_data_seek(),
mysql_select_db(), and
mysql_query().
For downward compatibility
mysql_numrows() can also be used. This is deprecated
however.