SYS_OP_ZONE_ID

Syntax

Purpose

SYS_OP_ZONE_ID takes as its argument a rowid and returns a zone ID. The rowid identifies a row in a table. The zone ID identifies the set of contiguous disk blocks, called the zone, that contains the row. The function returns a NUMBER value.

The SYS_OP_ZONE_ID function is used when creating a zone map with the CREATE MATERIALIZED ZONEMAP statement. You must specify SYS_OP_ZONE_ID in the SELECT and GROUP BY clauses of the defining subquery of the zone map.

For rowid, specify the ROWID pseudocolumn of the fact table of the zone map.

Use schema and table to specify the schema and name of the fact table, or t_alias to specify the table alias for the fact table. The specification of these parameters depends on the FROM clause in the defining subquery of the zone map:

• If the FROM clause specifies a table alias for the fact table, then you must also specify the table alias (t_alias) in SYS_OP_ZONE_ID.

• If the FROM clause does not specify a table alias for the fact table, then use table to specify the name of the fact table. You can use the schema qualifier if the fact table is in a schema other than your own. If you omit schema, then the database assumes the fact table is in your own schema. If the FROM clause specifies only one table (the fact table) then you need not specify schema or table.

The optional scale parameter represents the scale of the zone map. It is not necessary to specify this parameter because, by default, SYS_OP_ZONE_ID uses the scale of the zone map being created. If you do specify scale, then it must match the scale of the zone map being created. Refer to the SCALE clause of CREATE MATERIALIZED ZONEMAP for information on specifying the scale of a zone map.

Examples

The following example uses the SYS_OP_ZONE_ID function when creating a basic zone map that tracks the column time_id of the fact table sales. The scale of the zone map is the default value of 10. Therefore, the SYS_OP_ZONE_ID function will default to a scale value of 10.

CREATE MATERIALIZED ZONEMAP sales_zmap
AS
  SELECT SYS_OP_ZONE_ID(rowid), MIN(time_id), MAX(time_id)
  FROM sales
  GROUP BY SYS_OP_ZONE_ID(rowid);

The following example is similar to the previous example, except that the scale of the zone map being created is specified as 8. Therefore, the SYS_OP_ZONE_ID function will default to a scale value of 8.

CREATE MATERIALIZED ZONEMAP sales_zmap
SCALE 8
AS
  SELECT SYS_OP_ZONE_ID(rowid), MIN(time_id), MAX(time_id)
  FROM sales
  GROUP BY SYS_OP_ZONE_ID(rowid);

The following example returns an error because the scale of the zone map being created is specified as 8, which does not match the scale argument of 12 specified in the SYS_OP_ZONE_ID function.

CREATE MATERIALIZED ZONEMAP sales_zmap
SCALE 8
AS
  SELECT SYS_OP_ZONE_ID(rowid,12), MIN(time_id), MAX(time_id)
  FROM sales
  GROUP BY SYS_OP_ZONE_ID(rowid,12);

The following example creates a join zone map. The fact table is sales and the dimension tables are products and customers. Because the table alias s is specified for the fact table in the FROM clause, the table alias s is also specified in the SYS_OP_ZONE_ID function.

CREATE MATERIALIZED ZONEMAP sales_zmap
AS
  SELECT SYS_OP_ZONE_ID(s.rowid),
         MIN(prod_category), MAX(prod_category),
         MIN(country_id), MAX(country_id)
  FROM sales s, products p, customers c
  WHERE s.prod_id = p.prod_id(+) AND
        s.cust_id = c.cust_id(+)
  GROUP BY SYS_OP_ZONE_ID(s.rowid);