re：请教高手们PostgreSQL里面NULL::varchar是什么意思?下面有详细整条语句~请高手们进来帮忙~

SELECT batch_sbt,
       catch_file_name,
       '0' AS status_flg,
       to_char(proc_start_ymd, 'YYYY/MM/DD HH24:MI:SS') AS proc_start_ymd,
       NULL::varchar AS proc_end_ymd,
       batch_ins_user_name,
       NULL AS archive_cnt,
       NULL AS archive_money,
       NULL AS total_cnt,
       '' AS log_file_name,
       '' AS fm_status_flg,
       '' AS cancel_flg,
       '' AS file_archive_mng_id
  FROM batch_mng AS BM
 WHERE to_char(BM.proc_start_ymd, 'YYYYMMDD') between '20060803' AND
       '20060803'
 ORDER BY proc_start_ymd DESC, proc_end_ymd DESC, batch_sbt ASC

这句SQL语句是PostgreSQL里面的,我现在想移植到ORACLE里面去,我该怎么改?请指教~ 

元组中的proc_end_ymd属性可NULL 或者 是varchar类型在本例中即为,技术时间可以为空，或是varchar类型，在后来如果插入该属性指，那么该属性以varchar类型进行重载
－－ Ｆｌｙｘｘ  @2006-11-28 13:03:24  @http://blog.csdn.net/flyxx/