title: how greenplum partition support varchar datatype
body: <p>Script is:</p>
  <pre><code>create table T_RH_AJ_XW_JCJJJ2 (
     ZJ_ID                VARCHAR(32)          not null,
     JJ_RQ                VARCHAR(32),
     RK_SJ                TIMESTAMP,
     GX_SJ                TIMESTAMP,
     SJZT_W               VARCHAR(32)
  )
  distributed by (ZJ_ID)
  partition by range (JJ_RQ)
  (
       START ('2012-08-11'::date) END ('2012-08-12'::date)
       EVERY ( INTERVAL '1 day')
  );   
  </code></pre>
  <p>I want partition use varchar column（JJ_RQ datatype, and this column value is '2020-11-08';
  but this is a error:</p>
  <blockquote>
  <p>error is 'operator does not exist: character varying + interval, No operator matches the given name and argument type(s). You might need to add explicit type casts.</p>
  </blockquote>