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Oracle Tips by Burleson

Dropping a Cluster and Declustering Tables

As with the creation of clusters, dropping a cluster is a multistep function. The first step is to drop the tables in the cluster using the DROP TABLE command. Next, the cluster is dropped with the DROP CLUSTER command. An INCLUDING TABLES clause allows the DBA to drop both the cluster and tables at the same time. The format of the command can be found on the documentation website at technet.oracle.com.

Rather than dropping a cluster’s tables completely, it may be desirable to decluster them and then just drop the cluster and cluster index with the DROP CLUSTER command. The procedure to decluster a table follows:

1. Create a new table that is a mirror of the existing clustered table—except , of course, it isn’t clustered.

CREATE TABLE new table

AS SELECT * FROM cluster table

Tip

Remember that “new table” is a different name from “cluster table.”

2. Drop the clustered table.

DROP TABLE cluster table

3. Rename the replacement table.

RENAME new table TO cluster table

4. Reassign all grants; create required indexes and constraints.

Tip

In the sample SQL scripts zip file on the Wiley website there is a dynamic SQL script that will create a grant script for a specified database object. The script must, of course, be run before the object is dropped.

5. Drop the cluster.

See Code Depot