ORA-01439: column to be modified must be empty to change datatype

修改数据库字段类型，但是由于数据表已经存在数据，无法修改；

显示错误：ORA-01439: column to be modified must be empty to change datatype

 alter table USERS add tmp_col NUMBER(1);-- 添加临时列

update USERS set tmp_col = CUSTOMER_MARITAL_STATUS ; --将目标字段中数据加入到临时列中

update USERS set CUSTOMER_MARITAL_STATUS = null; --将目标字段数据清空

alter table USERS modify ( CUSTOMER_MARITAL_STATUS NUMBER(1)); --更改目标字段类型

update USERS set CUSTOMER_MARITAL_STATUS = tmp_col; --将临时列数据加回到目标字段中

alter table USERS drop column tmp_col; --清除临时列

SELECT DISTINCT CUSTOMER_MARITAL_STATUS  FROM USERS;
SELECT DISTINCT tmp_col  FROM USERS;