Explain EXPLAIN (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 3)
    ExpressionList (children 1)
     Function count (children 1)
      ExpressionList
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier users1 (alias u1)
    Function not (children 1)
     ExpressionList (children 1)
      Function exists (children 1)
       ExpressionList (children 1)
        Subquery (children 1)
         SelectWithUnionQuery (children 1)
          ExpressionList (children 1)
           SelectQuery (children 3)
            ExpressionList (children 1)
             Asterisk
            TablesInSelectQuery (children 1)
             TablesInSelectQueryElement (children 1)
              TableExpression (children 1)
               TableIdentifier users2 (alias u2)
            Function notEquals (children 1)
             ExpressionList (children 2)
              Identifier u1.uid
              Identifier u2.uid
