Using a WHERE Clause
A cache table definition in a CREATE CACHE GROUP
statement can
contain a WHERE
clause to restrict the rows to cache in the TimesTen
database for particular cache group types.
You can also specify a WHERE
clause in a LOAD CACHE GROUP
, UNLOAD CACHE GROUP
, REFRESH CACHE GROUP
or FLUSH CACHE GROUP
statement for particular cache group types. Some statements, such as LOAD CACHE GROUP
and REFRESH CACHE GROUP
, may result in concatenated WHERE
clauses in which the WHERE
clause for the cache table definition is evaluated before the WHERE
clause in the LOAD CACHE GROUP
or REFRESH CACHE GROUP
statement.
The following restrictions apply to WHERE
clauses used in cache table definitions and cache group operations:
-
WHERE
clauses can only be specified in the cache table definitions of aCREATE CACHE GROUP
statement for read-only and user managed cache groups. -
A
WHERE
clause can be specified in aLOAD CACHE GROUP
statement except on a static cache group with autorefresh.See Manually Loading and Refreshing a Cache Group for more information about the
LOAD CACHE GROUP
. -
A
WHERE
clause can be specified in aREFRESH CACHE GROUP
statement except on a cache group with autorefresh.See Manually Loading and Refreshing a Cache Group for more information about the
REFRESH CACHE GROUP
statement. -
A
WHERE
clause can be specified in aFLUSH CACHE GROUP
statement on a user managed cache group that allows committed changes on the TimesTen cache tables to be flushed to the cached Oracle Database tables.See Flushing a User Managed Cache Group for more information about the
FLUSH CACHE GROUP
statement. -
WHERE
clauses in aCREATE CACHE GROUP
statement cannot contain a subquery. Therefore, eachWHERE
clause cannot reference any table other than the one in its cache table definition. However, aWHERE
clause in aLOAD CACHE GROUP
,UNLOAD CACHE GROUP
,REFRESH CACHE GROUP
orFLUSH CACHE GROUP
statement may contain a subquery. -
A
WHERE
clause in aLOAD CACHE GROUP
,REFRESH CACHE GROUP
orFLUSH CACHE GROUP
statement can reference only the root table of the cache group, unless theWHERE
clause contains a subquery. -
All tables and columns referenced in
WHERE
clauses when creating, loading, refreshing, unloading or flushing the cache group must be fully qualified. For example:owner
.
table_name
andowner
.
table_name
.
column_name
Proper Placement of WHERE Clause in a CREATE CACHE GROUP Statement
In a multiple-table cache group, a WHERE
clause in a particular table definition should not reference any table in the cache group other than the table itself. For example, the following CREATE CACHE GROUP
statements are valid:
CREATE READONLY CACHE GROUP customer_orders FROM sales.customer (cust_num NUMBER(6) NOT NULL, region VARCHAR2(10), name VARCHAR2(50), address VARCHAR2(100), PRIMARY KEY(cust_num)) WHERE (sales.customer.cust_num < 100), sales.orders (ord_num NUMBER(10) NOT NULL, cust_num NUMBER(6) NOT NULL, when_placed DATE NOT NULL, when_shipped DATE NOT NULL, PRIMARY KEY(ord_num), FOREIGN KEY(cust_num) REFERENCES sales.customer(cust_num));
CREATE READONLY CACHE GROUP customer_orders FROM sales.customer (cust_num NUMBER(6) NOT NULL, region VARCHAR2(10), name VARCHAR2(50), address VARCHAR2(100), PRIMARY KEY(cust_num)), sales.orders (ord_num NUMBER(10) NOT NULL, cust_num NUMBER(6) NOT NULL, when_placed DATE NOT NULL, when_shipped DATE NOT NULL, PRIMARY KEY(ord_num), FOREIGN KEY(cust_num) REFERENCES sales.customer(cust_num)) WHERE (sales.orders.cust_num < 100);
The following statement is not valid because the WHERE
clause in the child table's definition references its parent table:
CREATE READONLY CACHE GROUP customer_orders FROM sales.customer (cust_num NUMBER(6) NOT NULL, region VARCHAR2(10), name VARCHAR2(50), address VARCHAR2(100), PRIMARY KEY(cust_num)), sales.orders (ord_num NUMBER(10) NOT NULL, cust_num NUMBER(6) NOT NULL, when_placed DATE NOT NULL, when_shipped DATE NOT NULL, PRIMARY KEY(ord_num), FOREIGN KEY(cust_num) REFERENCES sales.customer(cust_num)) WHERE (sales.customer.cust_num < 100);
Similarly, the following statement is not valid because the WHERE
clause in the parent table's definition references its child table:
CREATE READONLY CACHE GROUP customer_orders FROM sales.customer (cust_num NUMBER(6) NOT NULL, region VARCHAR2(10), name VARCHAR2(50), address VARCHAR2(100), PRIMARY KEY(cust_num)) WHERE (sales.orders.cust_num < 100), sales.orders (ord_num NUMBER(10) NOT NULL, cust_num NUMBER(6) NOT NULL, when_placed DATE NOT NULL, when_shipped DATE NOT NULL, PRIMARY KEY(ord_num), FOREIGN KEY(cust_num) REFERENCES sales.customer(cust_num));
Referencing Oracle Database PL/SQL Functions in a WHERE Clause
A user-defined PL/SQL function in the Oracle database can be invoked indirectly in a
WHERE
clause within a CREATE CACHE GROUP
, LOAD CACHE
GROUP
, or REFRESH CACHE GROUP
(for dynamic cache groups only)
statement.
After creating the function, create a public synonym for the function. Then
grant the EXECUTE
privilege on the function to PUBLIC
.
For example, in the Oracle database:
CREATE OR REPLACE FUNCTION get_customer_name (c_num sales.customer.cust_num%TYPE) RETURN VARCHAR2 IS c_name sales.customer.name%TYPE; BEGIN SELECT name INTO c_name FROM sales.customer WHERE cust_num = c_num; RETURN c_name; END get_customer_name; CREATE PUBLIC SYNONYM retname FOR get_customer_name; GRANT EXECUTE ON get_customer_name TO PUBLIC;
Then in the TimesTen database, for example, you can create a cache group with a WHERE
clause that references the Oracle Database public synonym that was created for the function:
CREATE READONLY CACHE GROUP top_customer FROM sales.customer (cust_num NUMBER(6) NOT NULL, region VARCHAR2(10), name VARCHAR2(50), address VARCHAR2(100), PRIMARY KEY(cust_num)) WHERE sales.customer.name = retname(100);
For cache group types that allow a WHERE
clause on a LOAD CACHE GROUP
or REFRESH CACHE GROUP
statement, you can invoke the function indirectly by referencing the public synonym that was created for the function. For example, you can use the following LOAD CACHE GROUP
statement to load the AWT cache group new_customers
:
LOAD CACHE GROUP new_customers WHERE name = retname(101) COMMIT EVERY 0 ROWS;