On Mon, Apr 27, 2009 at 03:13:09PM +0200, Matej Hasul wrote:
> Hello, I started working on migrating tables to mysql.
>
> Data types conversion looks like this:
>
> varchar2 -> varchar
> number -> numeric
> date -> timestamp
>
> Following problems emerged:
> 1. Mysql doesn`t support user defined data type. So I have no idea what to
> do with evr_t.
Please check what the deal with evr_t in PostgreSQL port was. IIRC,
the type is used for collation and presentation, so you should be able
to replace it with plain table and a couple of functions.
> 2. Mysql doesn`t support nested tables. For example something like "create
> or replace type channel_name_t as table of varchar(64)". Does anyone know
> some workaround?
Check if that type is needed at all. Looking around the source code,
it is only used in the channel_name_join function, and that one does
not seem to be called anywhere. So it both looks like a dead code to
me, which should be removed from the Oracle schema as well.
> 3. Check constraint not working. According to mysql documentation - "The
> CHECK clause is parsed but ignored by all storage engines".
> Workaround: Use before-insert-or-update trigger to implement check
> constraint.
OK.
> 4. Create table test(date1 date default (sysdate), date2 date default
> (sysdate)) will not work in mysql, because there can be only one date column
> with default clause.
> Workaround: Use before-insert-or-update trigger to set actual date(s).
OK.
> 5. Missing sequence in mysql.
> Workaround: One option is to use AUTO_INCREMENT and LAST_INSERT_ID().
> Another option is to create table holding sequence number and create
> procedures curval('seq_name') and nextval('seq_name').
With the table-holding-sequence-values approach (and I'm not sure
about the first one), keep in mind that it will be
transaction-aware -- if you rollback, you will get the same value next
time. That might or might not be a problem. Also, for the same reason,
the sessions will likely serialize on that table.
--
Jan Pazdziora
Senior Software Engineer, Satellite Engineering, Red Hat
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