|Oracle® Database SQL Reference
10g Release 1 (10.1)
Part Number B10759-01
DIMENSION statement to create a dimension. A dimension defines a parent-child relationship between pairs of column sets, where all the columns of a column set must come from the same table. However, columns in one column set (called a level) can come from a different table than columns in another set. The optimizer uses these relationships with materialized views to perform query rewrite. The SQLAccess Advisor uses these relationships to recommend creation of specific materialized views.
Note:Oracle Database does not automatically validate the relationships you declare when creating a dimension. To validate the relationships specified in the
To create a dimension in your own schema, you must have the
DIMENSION system privilege. To create a dimension in another user's schema, you must have the
DIMENSION system privilege. In either case, you must have the
SELECT object privilege on any objects referenced in the dimension.
Specify the schema in which the dimension will be created. If you do not specify
schema, then Oracle Database creates the dimension in your own schema.
Specify the name of the dimension. The name must be unique within its schema.
level_clause defines a level in the dimension. A level defines dimension hierarchies and attributes.
Specify the name of the level.
Specify the columns in the level. You can specify up to 32 columns. The tables you specify in this clause must already exist.
All of the columns in a level must come from the same table.
If columns in different levels come from different tables, then you must specify the
The set of columns you specify must be unique to this level.
The columns you specify cannot be specified in any other dimension.
level_column must be non-null. However, these columns need not have
hierarchy_clause defines a linear hierarchy of levels in the dimension. Each hierarchy forms a chain of parent-child relationships among the levels in the dimension. Hierarchies in a dimension are independent of each other. They may, but need not, have columns in common.
Each level in the dimension should be specified at most once in this clause, and each level must already have been named in the
Specify the name of the hierarchy. This name must be unique in the dimension.
Specify the name of a level that has an n:1 relationship with a parent level. That is, the
child_level cannot be null, and each
child_level value uniquely determines the value of the next named
If the child
level_table is different from the parent
level_table, then you must specify a join relationship between them in the
Specify the name of a level.
dimension_join_clause lets you specify an inner equijoin relationship for a dimension whose columns are contained in multiple tables. This clause is required and permitted only when the columns specified in the hierarchy are not all in the same table.
Specify one or more columns that are join-compatible with columns in the parent level.
If you do not specify the schema and table of each
child_column, then the schema and table are inferred from the
OF relationship in the
hierarchy_clause. If you do specify the schema and column of a
child_key_column, then the schema and table must match the schema and table of columns in the child of
parent_level in the
Specify the name of a level.
You can specify only one
dimension_join_clause for a given pair of levels in the same hierarchy.
child_key_columns must be non-null, and the parent key must be unique and non-null. You need not define constraints to enforce these conditions, but queries may return incorrect results if these conditions are not true.
Each child key must join with a key in the
Self-joins are not permitted. That is, the
child_key_columns cannot be in the same table as
All of the child key columns must come from the same table.
The number of child key columns must match the number of columns in
parent_level, and the columns must be joinable.
You cannot specify multiple child key columns unless the parent level consists of multiple columns.
attribute_clause lets you specify the columns that are uniquely determined by a hierarchy level. The columns in
level must all come from the same table as the
dependent_columns need not have been specified in the
For example, if the hierarchy levels are
city might determine
state might determine
country might determine
This clause lets you specify an attribute name for one or more level-to-column relations. The type of attribute you create with this clause is not different from the type of attribute created using the
attribute_clause. The only difference is that this clause lets you assign a name to the attribute that is different from the level name.
This statement was used to create the
customers_dim dimension in the sample schema
CREATE DIMENSION customers_dim LEVEL customer IS (customers.cust_id) LEVEL city IS (customers.cust_city) LEVEL state IS (customers.cust_state_province) LEVEL country IS (countries.country_id) LEVEL subregion IS (countries.country_subregion) LEVEL region IS (countries.country_region) HIERARCHY geog_rollup ( customer CHILD OF city CHILD OF state CHILD OF country CHILD OF subregion CHILD OF region JOIN KEY (customers.country_id) REFERENCES country ) ATTRIBUTE customer DETERMINES (cust_first_name, cust_last_name, cust_gender, cust_marital_status, cust_year_of_birth, cust_income_level, cust_credit_limit) ATTRIBUTE country DETERMINES (countries.country_name) ;
extended_attribute_clause could have been used instead of the
attribute_clause, as shown in the following example:
CREATE DIMENSION customers_dim LEVEL customer IS (customers.cust_id) LEVEL city IS (customers.cust_city) LEVEL state IS (customers.cust_state_province) LEVEL country IS (countries.country_id) LEVEL subregion IS (countries.country_subregion) LEVEL region IS (countries.country_region) HIERARCHY geog_rollup ( customer CHILD OF city CHILD OF state CHILD OF country CHILD OF subregion CHILD OF region JOIN KEY (customers.country_id) REFERENCES country ) ATTRIBUTE customer_info LEVEL customer DETERMINES (cust_first_name, cust_last_name, cust_gender, cust_marital_status, cust_year_of_birth, cust_income_level, cust_credit_limit) ATTRIBUTE country DETERMINES (countries.country_name) ;