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mysql_use_result()
MYSQL_RES *mysql_use_result(MYSQL *mysql)
You must call mysql_store_result()
or mysql_use_result()
for
every query that successfully retrieves data (SELECT
, SHOW
,
DESCRIBE
, EXPLAIN
).
mysql_use_result()
initiates a result set retrieval but does not
actually read the result set into the client like mysql_store_result()
does. Instead, each row must be retrieved individually by making calls to
mysql_fetch_row()
. This reads the result of a query directly from the
server without storing it in a temporary table or local buffer, which is
somewhat faster and uses much less memory than mysql_store_result()
.
The client will allocate memory only for the current row and a communication
buffer that may grow up to max_allowed_packet
bytes.
On the other hand, you shouldn't use mysql_use_result()
if you are
doing a lot of processing for each row on the client side, or if the output
is sent to a screen on which the user may type a ^S
(stop scroll).
This will tie up the server and prevent other threads from updating any
tables from which the data is being fetched.
When using mysql_use_result()
, you must execute
mysql_fetch_row()
until a NULL
value is returned, otherwise, the
unfetched rows will be returned as part of the result set for your next
query. The C API will give the error Commands out of sync; you can't
run this command now
if you forget to do this!
You may not use mysql_data_seek()
, mysql_row_seek()
,
mysql_row_tell()
, mysql_num_rows()
, or
mysql_affected_rows()
with a result returned from
mysql_use_result()
, nor may you issue other queries until the
mysql_use_result()
has finished. (However, after you have fetched all
the rows, mysql_num_rows()
will accurately return the number of rows
fetched.)
You must call mysql_free_result()
once you are done with the result
set.
A MYSQL_RES
result structure. NULL
if an error occurred.
mysql_use_result()
resets mysql_error
and
mysql_errno
if it succeeds.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
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