Re: Com_empty_query

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 <[email protected]> wrote:
> 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%';
> +-----------------+-------+
> | Variable_name   | Value |
> +-----------------+-------+
> | Com_empty_query | 0     |
> +-----------------+-------+
> 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%';
> +-----------------+-------+
> | Variable_name   | Value |
> +-----------------+-------+
> | Com_empty_query | 0     |
> +-----------------+-------+
> 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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>



-- 
Eric Bergen
[email protected]
http://www.ebergen.net

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