pg_free_result() only needs to
be called if you are worried about using too much memory
while your script is running. All result memory will
automatically be freed when the script is finished. But, if
you are sure you are not going to need the result data
anymore in a script, you may call
pg_free_result() with the
result resource as an argument and the associated
result memory will be freed. 成功回傳TRUE失敗回傳FALSE。
注: This function used to be called pg_freeresult().
See also pg_query().