Change column type in hive

Question

I just started learning hive yesterday and I am stuck on changing the type of a column in hive. I wanted to ask if the changing of column type has some kind of restriction on them because I can only do specific type of changes like I can convert int to double, string to double, double to string but I cant change string to int, double to int.

ALTER TABLE student CHANGE rollno rollno int;
FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. Unable to alter table. The following columns have types incompatible with the existing columns in their respective positions :
rollno

hive> DESCRIBE FORMATTED student
> ;
OK
# col_name              data_type               comment             

rollno                  int                                         
name                    string                                      
phno                    string                                      
city                    string   

    ALTER TABLE student CHANGE rollno rollno double;
OK
Time taken: 0.144 seconds

ALTER TABLE student CHANGE rollno rollno int;

FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. Unable to alter table. The following columns have types incompatible with the existing columns in their respective positions :

rollno

Cant do with strings either. So please guide me towards the answer as I cant seem to find anything through google.

Answer 1

If you just want to change the column type，not caring about implicit conversions for example,the old columns type is wrong.

You can try this:

set hive.metastore.disallow.incompatible.col.type.changes=false;