MySQL 5.6 C API Developer Guide
int mysql_next_result(MYSQL *mysql)
mysql_next_result()
is used
when you execute multiple statements specified as a single
statement string, or when you use
CALL
statements to execute
stored procedures, which can return multiple result sets.
mysql_next_result()
reads the
next statement result and returns a status to indicate whether
more results exist. If
mysql_next_result()
returns an
error, there are no more results.
Before each call to
mysql_next_result()
, you must
call mysql_free_result()
for
the current statement if it is a statement that returned a
result set (rather than just a result status).
After calling
mysql_next_result()
the state
of the connection is as if you had called
mysql_real_query()
or
mysql_query()
for the next
statement. This means that you can call
mysql_store_result()
,
mysql_warning_count()
,
mysql_affected_rows()
, and so
forth.
If your program uses CALL
statements to execute stored procedures, the
CLIENT_MULTI_RESULTS
flag must be enabled.
This is because each CALL
returns a result to indicate the call status, in addition to
any result sets that might be returned by statements executed
within the procedure. Because
CALL
can return multiple
results, process them using a loop that calls
mysql_next_result()
to
determine whether there are more results.
CLIENT_MULTI_RESULTS
can be enabled when
you call mysql_real_connect()
,
either explicitly by passing the
CLIENT_MULTI_RESULTS
flag itself, or
implicitly by passing
CLIENT_MULTI_STATEMENTS
(which also enables
CLIENT_MULTI_RESULTS
). In MySQL
5.6, CLIENT_MULTI_RESULTS
is
enabled by default.
It is also possible to test whether there are more results by
calling mysql_more_results()
.
However, this function does not change the connection state,
so if it returns true, you must still call
mysql_next_result()
to advance
to the next result.
For an example that shows how to use
mysql_next_result()
, see
Chapter 16, C API Multiple Statement Execution Support.
Return Value | Description |
---|---|
0 | Successful and there are more results |
-1 | Successful and there are no more results |
>0 | An error occurred |
Commands were executed in an improper order. For example,
if you did not call
mysql_use_result()
for a
previous result set.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.