更新记录失败，提示重复输入错误

Question

CREATE TABLE `placements` (
  ......
  ......,
  PRIMARY KEY (`pl_id`),
  KEY `cur3` (`currency`),
  KEY `pl2` (`date_arranged`),
  KEY `pl3` (`start_date`,`end_date`),
  KEY `pla_peo_id` (`peo_id`),
  KEY `pla_placed_with` (`placed_with`),
  KEY `pla_reh2` (`remind_agent`,`status`,`end_date`),
  KEY `reh_temp2` (`parent_id`),
  KEY `pl_id` (`pl_id`),
  CONSTRAINT `pla_comp_fk1` FOREIGN KEY (`placed_with`) REFERENCES `companies` (`pid`),
  CONSTRAINT `pla_con_fk1` FOREIGN KEY (`peo_id`) REFERENCES `contractors` (`pid`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8

我有上面的表结构。我想更新pl_id = 320636的表格，并将end_date设置为新值。

update placements set end_date = '2016-03-09 00:00:00' where pl_id = '320636'

给予重复条目＆＃39; 320636-2016-02-15 00：00：00＆＃39;关键＆＃39; PRIMARY＆＃39;错误。

我试图删除主键但没有运气。请帮帮我吗？