Hi,
I was trying to find out what would trigger the counter on Com_empty_query and my two test cases do not trigger it:

mysql> SHOW STATUS LIKE 'Com_empty%';
+-----------------+-------+
1 row in set (0.00 sec)

mysql> SELECT * FROM foo WHERE bar=2;
Empty set (0.03 sec)

mysql> ;
ERROR:
No query specified

mysql> SHOW STATUS LIKE 'Com_empty%';
+-----------------+-------+
1 row in set (0.00 sec)

Looking at the source, it seems to get triggered on an END_OF_INPUT in the query section of 'sql_yacc.yy' (assuming the query is syntactically correct). sql_lex.cc is the only instance that returns an END_OF_INPUT (after a lip->eof()), but I can't seem to trigger it.

Is this triggered on a breakdown from the client, or on a certain type of (reproducible) query?

Thanks,
Derek Downey
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I think there are a few things going on. The first is that the command
line client is returning no query specified which means it didn't send
anything to the server. I wrote a small C app to send an empty query
to the server and it returns a "Query was empty" error then does a
show status on the same connection to check the counter. The counter
isn't incremented. I checked the source and the only increment I see
for empty_queries happens at the end of execute_sqlcom_select which
won't get called on an empty query. I think it needs to be incremented
in case SQLCOM_EMPTY_QUERY: in sql_parse.cc

Here is my small app for reference:

#include <stdio.h>
#include <string.h>
#include <mysql.h>

int main() {
MYSQL con;
MYSQL_RES *res;
MYSQL_ROW row;
char show_query[] = "show status like '%empty%'";
int num_fields, i;
mysql_init(&con);

if (!(mysql_real_connect(&con, "", "root", "", "test", 3306,
"/home/ebergen/store/mysql/standalone_mariadb/mysql.sock", 0)))
{
printf("Connection failed with %s\n", mysql_error(&con));
return 1;
}

if ((mysql_real_query(&con, "", 0)))
{
printf("Query failed with %s\n", mysql_error(&con));
// return 1;
}


if (mysql_real_query(&con, show_query, strlen(show_query)))
{
printf("Show query failed with %s\n", mysql_error(&con));
return 1;
}

res = mysql_store_result(&con);
num_fields = mysql_num_fields(res);

while ((row = mysql_fetch_row(res))) {
for (i = 0; i < num_fields; i++)
{
printf("%s\n", (char *)row[i]);
}
}

return 0;
}

On Thu, Oct 6, 2011 at 11:26 AM, Derek Downey <derek (AT) orange-pants (DOT) com> wrote:


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Eric Bergen
eric.bergen (AT) gmail (DOT) com
http://www.ebergen.net

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