Create a new calculated field using two fields in a table in the script

[mayuranp]

I have simplified my query.

Let's say I have a table with columns A,B,C already loaded.

Now I want to create a new column 'D' in this table by adding B+C.

I know it can be done as below, but don't want to create another table.

NewTable:

LOAD *,

          B+C as D

RESIDENT OldTable;

DROP TABLE OldTable;

Another question, if the above is the only method, is it the most efficient operation considering the table can have a million+ records.

Thanks

[sunny_talwar]

You don't have to do this in a resident load... you can do this in your first OldTable....

OldTable:

LOAD A,

     B,

     C,

     B+C as D

FROM ....;

[mayuranp]

Yes, but my query is the table is already loaded and I cannot alter that.

In my case the table is already loaded from few qvd files using concatenation and joins. Now I want to add a new field.

[sunny_talwar]

what do you mean it is already loaded? You will reload everything again to add the new column, right? Are you not planning to reload your application on a fixed schedule?

[rubenmarin]

Hi Mayuran, you can rename the old table to keep to keep the original name in the new table:

Rename oldTableName to TableNameToDrop:

oldTableName:
LOAD ..
Resident TableNameToDrop;

DROP TableNameToDrop;

[maxgro]

if your table has a primary key (pk) you can use a left join

ie if A is your pk

left join (OldTable) load

     A,

     B+C as D

resident OldTable;