The following is an example of how one could send logs to mysql. If you have specific logs that you want to save in an SQL for some odd reason ( eg: you work for an old company that goes about things in archaic ways ).

gistfile1.sql

-- NB '%{@type}' must be the same as table_name
-- create database logstash;
CREATE TABLE table_name (
    table_name_id int(8) unsigned NOT NULL AUTO_INCREMENT,
    logtime datetime DEFAULT NULL,
    tags varchar(255) DEFAULT NULL,
    message varchar(255) DEFAULT NULL,
   PRIMARY KEY (table_name_id)
);

GRANT  INSERT,SELECT  ON logstash.* TO logstash@localhost IDENTIFIED BY 'mysqlpasswd'; 

gistfile2.sh

#!/bin/sh
# a cheap and dirty example of how this can be done
#   if you do this at home, be sure to be more elegant!
DATE=`echo $2| cut -dT -f2 | cut -d. -f1`
TIME=`echo $2| cut -dT -f1 `
TABLE="$1"
printf  " INSERT INTO  $TABLE SET  logtime='$TIME $DATE', tags='$3', message='$4';" > /tmp/mysql-logstash.pipe  

logstash2sql.sh

output {
  exec {
    type => "table_name"
    tags => "send2sql"
    command =>  "/opt/logstash/bin/write2mysqlpipe.sh  '%{@type}' '%{@timestamp}'  '%{@tags}', '%{@message}'"
   }
}

mysql_pipemaker.sh

#!/bin/sh
#  Run this first to create a pipe to your MySQL server
#
if [ ! -e /tmp/mysql-logstash.pipe ] ;then
  mkfifo /tmp/mysql-logstash.pipe
fi

while [ -e /tmp/mysql-logstash.pipe ]; do
  mysql -u logstash  --password=mysqlpasswd  logstash < /tmp/mysql-logstash.pipe >/dev/null
done