Integrity constraint violation: 1052 Column 'uid' in on clause is ambiguous
You have to add alias in MigrateSQLMap

$this-&gt;map = new MigrateSQLMap($this-&gt;machineName,  
   array(  
       'uid' =&gt; array(  
           'type' =&gt; 'int',  
           'not null' =&gt; TRUE,  
           'alias' =&gt; 'u',  
       )  
   ),  
) ;