Re: Does Derby support ALTER TABLE DROP COLUMN?

[Dheeraj <dh...@daffodildb.com>]

Hi !!

 

I m Dheeraj  !!

May u help me about problem which is occur at time of using Apache Derby  !!

I m using Apache Derby Data Base for my project .

I want to information about alter a table !!

Like change column name or increase/ decrease the size of a column  !!

I want to information about how can I see the structure of a table through a
query or etc.

i.e how many columns currently present in a table  what their size & data type !!

 

Please give me list of what data type are convert to other data type !!

e.g 

varchar to bigint are convertible or not !!

bigint to varchar are convertible or not !!

These kind of list !!

 

Pls reply quickly as early as possible !!

 

Pls give me these information about Apache Derby !!

 

Bye !!

Questions about Derby (was Re: Does Derby support ALTER TABLE DROP COLUMN?)

["Jean T. Anderson" <jt...@bristowhill.com>]

Dheeraj wrote:
> ...
> I want to information about alter a table !!

The ALTER TABLE command is documented at
http://db.apache.org/derby/docs/10.1/ref/rrefsqlj81859.html .

> Like change column name or increase/ decrease the size of a column  !!

As the link above explains, you can increase the size of column, but not
decrease it. But there are some restrictions that are being addressed by
 DERBY-396 (http://issues.apache.org/jira/browse/DERBY-396) .

> I want to information about how can I see the structure of a table through a
> query or etc.
> 
> i.e how many columns currently present in a table  what their size & data type !!

Derby's 'dblook' utility outputs the DDL for objects in a database:

http://db.apache.org/derby/docs/10.1/tools/ctoolsgenddldb.html

DERBY-1164 (http://issues.apache.org/jira/browse/DERBY-1164) is a
feature request to add functionality to ij to output information.

Also, some of the GUI tools listed on the Wiki page below provide nice
viewing of database objects:

http://wiki.apache.org/db-derby/UsesOfDerby#ProductsByType

> Please give me list of what data type are convert to other data type !!

A table that shows which types can be explicitly converted ("cast") to
another is in the SQL Reference Guide:

http://db.apache.org/derby/docs/10.1/ref/rrefsqlj33562.html

And this page summarizes the data types that can be used for comparison,
sorting and ordering expressions:

http://db.apache.org/derby/docs/10.1/ref/rrefsqlj58560.html


>  ...
> Pls give me these information about Apache Derby !!

Much of the information you are looking for is available in the Derby
manuals, which you can access from the Derby web site:

http://db.apache.org/derby/manuals

I hope this helps.

regards,

 -jean