Changing Physical Schema

In addition to your initial superprojections, you can create new projections using the CREATE PROJECTION command. A single table can have multiple projections, if necessary.

Having multiple projections for the same table impedes data updates. Retain only the necessary projections in your production design.

If you want to replace a superprojection, a new superprojection must be created before the old one is removed.


  1. Review the existing projections in your Data Warehouse instance:

    SELECT * FROM projections p WHERE p.projection_schema = '[DW_ID]'
  2. Run the CREATE PROJECTION commands to create new projections. The projection is automatically populated with data after creation.

    Projection refresh must finish in 2 hours, otherwise the JDBC driver cancels the operation and the projection stays unrefreshed.

  3. Drop projections that are no longer necessary using the DROP PROJECTION command.

    You cannot drop a projection if it's the only superprojection.


Occasionally, the following error may occur when dropping a projection:

ROLLBACK: Projection cannot be dropped because history after AHM would be lost

In this case, try again later. If the problem persists, contact GoodData Customer Support.

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