Returns the number of rows deleted, inserted, or updated by an SQL statement.
To determine the number of rows that will be returned by a SELECT statement, issue SELECT COUNT(*) with the same predicates as your intended SELECT statement and retrieve the value.
If your application logic checks the number of rows returned by a SELECT
statement and branches if the number of rows is 0, consider modifying your
application to attempt to return the first row with one of
db2_fetch_array(), or db2_fetch_row(),
and branch if the fetch function returns
If you issue a SELECT statement using a scrollable cursor, db2_num_rows() returns the number of rows returned by the SELECT statement. However, the overhead associated with scrollable cursors significantly degrades the performance of your application, so if this is the only reason you are considering using scrollable cursors, you should use a forward-only cursor and either call SELECT COUNT(*) or rely on the boolean return value of the fetch functions to achieve the equivalent functionality with much better performance.