#!/bin/bash

##
## create table t1 and t2 (identical definition):
##
mysql -B test <<'EOF'
drop table if exists t1;
drop table if exists t2;

CREATE TABLE t1 (
  `knr` int(11) unsigned default NULL,
  `em` varchar(255) default NULL,
  UNIQUE KEY `knr` (`knr`),
  KEY `em` (`em`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_german2_ci;

CREATE TABLE t2 like t1;
EOF

##
## fill table with data:
##
max=100
i=0
while [ $i -lt $max ] ; do
  i=$(($i + 1))
  echo "insert into t1 values ($i, 'em$i');"
  echo "insert into t2 values ($i, 'em$i');"
done | mysql -B test 

##
## loop endless updates:
##
## print a dot on every update to have some progress indicator.
##
while true ; do

  mysql test -e "UPDATE t2 INNER JOIN t1 USING(knr) SET knr = NULL WHERE t1.em <> t2.em"
  echo -n .

done

exit 0