ALTER TABLE in Hypersonic SQL

Question

As we all know, Hypersonic SQL does not support the ALTER TABLE statement
yet, so the cool schema update feature of the schematool does not work.
However, it seems like it would be possible to achieve the same effect
with the following sequence of SQL statements (yes, I know it would be
really slow!):
1. Create a new temp table with all the columns of the original table plus
the new column(s).
2. SELECT INTO from the original table into the temp table.
3. Drop the original table.
4. Create a new table with the same name as the original table with all
the desired columns.
5. SELECT INTO from the temp table to the new table.
6. Drop the temp table.
Is there any way in a HSQLDictionary subclass to alter the generation of
the ALTER TABLE statements?
Thanks,
David A. King

Answer 1

Thanks for your help on this.
I just tried the following set of SQL statements to simulate an ALTER
TABLE:
// This is the original table
CREATE TABLE T1 (A VARCHAR PRIMARY KEY, B VARCHAR, C VARCHAR)
// Here are the statements to do an ALTER TABLE
SELECT * INTO T2 FROM T1
DROP TABLE T1
CREATE TABLE T1 (A VARCHAR PRIMARY KEY, B VARCHAR, C VARCHAR, D VARCHAR)
INSERT INTO T1 (A, B, C) SELECT A, B, C FROM T2
DROP TABLE T2
These statements work. What is needed to produce them is the original set
of column names (and definitions), in this example (A VARCHAR PRIMARY KEY,
B VARCHAR, C VARCHAR); and the new column definition, in this example (D
VARCHAR).
Thanks,
David
Marc Prud'hommeaux wrote:
David-
A quick test shows that this isn't going to be quite so easy: 'SELECT
INTO' requires that the table name be a new table, not an already
existing one. And 'INSERT INTO TABLE_A SELECT * FROM TABLE_B' will fail
if there are a different number of columns. Thus, the API would require
some additional metadata (about how many columns exist in the current
table) in order to be able to do this.
I have made a note of it in the RFE that I made for this.
Marc Prud'hommeaux <[email protected]> wrote:
David-
Interesting idea: we will look into doing that for the future. It would
be very nice if we could support schema migration on Hypersonic, since
it is very lightweight and flexible. I have made an enhancement request
at:
https://bugzilla.solarmetric.com/show_bug.cgi?id=160
If you want to give it a shot yourself, you can extends the
com.solarmetric.kodo.impl.jdbc.schema.dict.HSQLDictionary class and
override:
public String[] getAddColumnSQL (Column column)
and
public String[] getDropColumnSQL (Column column)
The methods should return an array of SQL statements that should be
executed to perform the add or drop.
David A. King <[email protected]> wrote:
As we all know, Hypersonic SQL does not support the ALTER TABLE statement
yet, so the cool schema update feature of the schematool does not work.
However, it seems like it would be possible to achieve the same effect
with the following sequence of SQL statements (yes, I know it would be
really slow!):
1. Create a new temp table with all the columns of the original table plus
the new column(s).
2. SELECT INTO from the original table into the temp table.
3. Drop the original table.
4. Create a new table with the same name as the original table with all
the desired columns.
5. SELECT INTO from the temp table to the new table.
6. Drop the temp table.
Is there any way in a HSQLDictionary subclass to alter the generation of
the ALTER TABLE statements?
Thanks,
David A. King
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com
Kodo Java Data Objects Full featured JDO: eliminate the SQL from your code
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com
Kodo Java Data Objects Full featured JDO: eliminate the SQL from your code