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Oracle® Database SQL Reference 10g Release 2 (10.2) Part Number B14200-02 |
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# XMLDATA Pseudocolumn

Oracle stores `XMLType` data either in LOB or object-relational columns, based on XMLSchema information and how you specify the storage clause. The `XMLDATA` pseudocolumn lets you access the underlying LOB or object relational column to specify additional storage clause parameters, constraints, indexes, and so forth.

Example The following statements illustrate the use of this pseudocolumn. Suppose you create a simple table of `XMLType`:

    CREATE TABLE xml_lob_tab of XMLTYPE;

The default storage is in a `CLOB` column. To change the storage characteristics of the underlying LOB column, you can use the following statement:

    ALTER TABLE xml_lob_tab MODIFY LOB (XMLDATA)
       (STORAGE (BUFFER_POOL DEFAULT) CACHE);

Now suppose you have created an XMLSchema-based table like the `xwarehouses` table created in "Using XML in SQL Statements". You could then use the `XMLDATA` column to set the properties of the underlying columns, as shown in the following statement:

    ALTER TABLE xwarehouses ADD (UNIQUE(XMLDATA."WarehouseId"));