Issue on column length changing in HANA

Question

Hi Experts,
I encounter the following issues.
1. Try to create a column table with a DATE type column, and insert some values.
CREATE COLUMN TABLE test1(D DATE);
INSERT INTO test1(D) VALUES (CURRENT_DATE);
SELECT D, length(D) FROM test1;
The result would be like:
D                      length(D)
Dec 8, 2014     10
2. Try to change the type of column D from DATE to NVARCHAR(8), and it did work.
ALTER TABLE TEST1 ALTER(D NVARCHAR(8));
SELECT D, length(D) FROM test1
The result would be like:
D                      length(D)
2014-12-08      10
3. Try to insert a string with more than 8 characters into table, but failed.
insert into TEST1 values(to_nvarchar(current_date));
Could not execute 'insert into TEST1 values(to_nvarchar(current_date))' in 258 ms 23 µs .
SAP DBTech JDBC: [274]: inserted value too large for column: Failed in "D" column with the value '2014-12-08'
Questions:
Why is it possible that HANA still keeps the original record of DATE type with length greater than 8(in this case 10) after the column type has changed to NVARCHAR(8)? I assume it would either not allow to change the column type from DATE to NVARCHAR(8) because it contains a record with length greater than 8, or it would just drop the record or change it to other format, something like that?
Appreciated for any input.
Thanks and Regards,
Aron

Answer 1

Dear Aron,
In the first step you inserted the current date and you got the result on select. in DB date is stored in internal format like 20141208. so the total length is 8.
In the second case you changed the type to CHAR 8 and the data stored in the DB is also having length of 8.
In the third case you tried to insert '2014-12-08', since the type is CHAR, now the length is of your input is 10, it will consider the - also. that is the reason for this error.  Not sure how you got the length 10 on select.
Regards,
Rahul