I need to add a new column to an existing table in my database.
The column should be placed in a specific position.
I know this can be done in two separate commands:
ALTER TABLE MYTABLE
ADD MYCOL INTEGER
ALTER TABLE MYTABLE
ALTER MYCOL POSITION 12
But is there a way to do this in just one?
I searched Interbase's documentation and found nothing that refers to this.
Thanks.
This is the correct syntax:
ALTER TABLE MYTABLE
ADD MYCOL INTEGER,
ALTER COLUMN MYCOL POSITION 12
Yes; you can chain one or more operations to the ALTER TABLE syntax.
See http://docwiki.embarcadero.com/InterBase/2020/en/ALTER_TABLE
Batsheva's answer above is correct.
Related
Hi I just added a new column Business_sys to my table my_table:
ALTER TABLE my_table ALTER business_sys TYPE set<text>;
But again I just droped this column name because I wanted to change the type of column:
ALTER TABLE my_table DROP business_sys;
Again when I tried to add the same colmn name with different type am getting error message
"Cannnot add a collection with the name business_sys because the collection with the same name and different type has already been used in past"
I just tried to execute this command to add a new column with different type-
ALTER TABLE my_table ADD business_sys list<text>;
What did I do wrong? I am pretty new to Cassandra. Any suggestions?
You're running into CASSANDRA-6276. The problem is when you drop a column in Cassandra that the data in that column doesn't just disappear, and Cassandra may attempt to read that data with its new comparator type.
From the linked JIRA ticket:
Unfortunately, we can't allow dropping a component from the comparator, including dropping individual collection columns from ColumnToCollectionType.
If we do allow that, and have pre-existing data of that type, C* simply wouldn't know how to compare those...
...even if we did, and allowed [users] to create a different collection with the same name, we'd hit a different issue: the new collection's comparator would be used to compare potentially incompatible types.
The JIRA suggests that this may not be an issue in Cassandra 3.x, but I just tried it in 3.0.3 and it fails with the same error.
What did I do wrong? I am pretty new to Cassandra. Any suggestions?
Unfortunately, the only way around this one is to use a different name for your new list.
EDIT: I've tried this out in Cassandra and ended up with inconsistent missing data. Best way to proceed is to change the column name as suggested in CASSANDRA-6276. And always follow documentation guidelines :)
-WARNING-
According to this comment from CASSANDRA-6276, running the following workaround is unsafe.
Elaborating on #masum's comment - it's possible to work around the limitation by first recreating the column with a non-collection type such as an int. Afterwards, you can drop and recreate again using the new collection type.
From your example, assuming we have a business_sys set:
ALTER TABLE my_table ADD business_sys set<text>;
ALTER TABLE my_table DROP business_sys;
Now re-add the column as int and drop it again:
ALTER TABLE my_table ADD business_sys int;
ALTER TABLE my_table DROP business_sys;
Finally, you can re-create the column with the same name but different collection type:
ALTER TABLE my_table ADD business_sys list<text>;
Cassandra doesn't allow you to recreate a column with the same name and the same datatype, but there is an workaround to fix it.
Once you have dropped the column with SET type, you can recreate it with only another "default" type such as varchar or interger.
After recreating with one of those types, you can drop the column once again and finally recreate with the proper type.
I illustrated it below
ALTER TABLE my_table DROP business_sys; # the drop you've done
ALTER TABLE my_table ADD business_sys varchar; # recreating with another type
ALTER TABLE my_table DROP business_sys; # dropping again
ALTER TABLE my_table ADD business_sys list<text>; # recreating with proper type
I want to retrieve all items within a specific column of a table.
In this scenario, I have 2 tables, The first table contains a primary key, and the second table contains a foreign key. a 1 to many relationship is set up for the tables respectively.
I want a function/way of retrieving all items within a column in table 2 that has a foreign key that matches the primary key in table 1.
One way of doing this is through a VLOOKUP, though surely through using DAX, or some other function set, I can exploit the relationship I have made in the DataModel to make this easier for me to do.
Why don't you just get the required data from the DB with a proper SELECT statement? Something like
SELECT column
FROM t1, t2
WHERE t1.key = t2.fkey
AND t1.key = 'whatever you search for';
Then you should get the data you want.
I need to add additional columns to a table in cassandra. But the existing table is not empty. Is there any way to update it in a simple way? Otherwise what is the best approach to add additional columns to a non empty table? thx in advance.
There's a good example of adding table columns to an existing table in the CQL documentation on ALTER. The following statement will add the column gravesite (with type varchar) to to the table addamsFamily:
ALTER TABLE addamsFamily ADD gravesite varchar;
I want to add columns dynamically to this column family via code using cql.
CREATE COLUMN FAMILY blog_entry
WITH comparator = UTF8Type
AND key_validation_class=UTF8Type
AND default_validation_class = UTF8Type;
how shall I do it?
This is becoming something of a FAQ, so I wrote an in-depth explanation: http://www.datastax.com/dev/blog/does-cql-support-dynamic-columns-wide-rows
For this to work you have to first alter the table to add column and then insert will start working. I tried the above on cqlsh and it worked.
alter table newdata add column name varchar;
Please refer below link too:
How to define dynamic column families in cassandra
ALTER TABLE blog_entry ADD newcolumnname text;
I need to query statement to list all tables from a database containing a given column name
in TransBase.
Thank you very much in advance.
select * from syscolumn col
inner join systable tbl on tbl.segno=col.tsegno
where col.cname like '%col_name%';
That was quick! For everybody that might need this in future.