title: Using SUBSTRING in JOIN condition
body: <p>SAP says that the function SUBSTRING is not known when activating this code:</p>
  <pre><code> SELECT a~client, a~loobj1, a~lotyp, a~proid, a~lockr, a~fdate, a~tdate, a~gpart, a~vkont, a~cond_loobj, 
          a~actkey, a~uname, a~adatum, a~azeit, a~protected, a~laufd, a~laufi
     FROM dfkklocks AS a
    INNER JOIN dfkkop AS b ON SUBSTRING( a~loobj1,1,12 ) = b~opbel
    WHERE b~augst = 9 AND a~lotyp  = '02'
     INTO CORRESPONDING FIELDS OF TABLE @gt_dfkklocks.
  </code></pre>