我想将数据类型从 String 至 TimeStamp 在Hive中，但下面的查询没有帮助。

ALTER TABLE so_wireless_cpu_utilization MODIFY start_time start_time TIMESTAMP;

它抛出以下错误：

Getting log thread is interrupted, since query is done!
Error: Error while compiling statement: FAILED: ParseException line 1:40 cannot recognize input near 'MODIFY' 'start_time' 'start_time' in alter table statement (state=42000,code=40000)
org.apache.hive.service.cli.HiveSQLException: Error while compiling statement: FAILED: ParseException line 1:40 cannot recognize input near 'MODIFY' 'start_time' 'start_time' in alter table statement
        at org.apache.hive.jdbc.Utils.verifySuccess(Utils.java:279)

此外，我尝试了以下查询，但也不起作用：

alter table so_wireless_ap_channels CHANGE load_date load_date String;

那么什么是转换 string 格式化为 timestamp 在 hive .