title: In case-when-then-else clause gives ERROR: more than one row returned by a subquery used as an expression. in postgresql
body: <p>On firing below query gives an ERROR:  more than one row returned by a subquery used as an expression.</p>
  
  <p><code>select case when (table_name_1.column_name = 'ABC')</code> <br>
  <code>then  (select column_name_2 from table_name_2 where column_name_3='XYZ')</code> <br>
   <code>else table_name_1.column_name end as result from table_name_1 ;</code><br> </p>