1. Cache Guide
  2. Defining Cache Groups
  3. Using a WHERE Clause

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 a CREATE CACHE GROUP statement for read-only and user managed cache groups.

  • A WHERE clause can be specified in a LOAD 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 a REFRESH 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 a FLUSH 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 a CREATE CACHE GROUP statement cannot contain a subquery. Therefore, each WHERE clause cannot reference any table other than the one in its cache table definition. However, a WHERE clause in a LOAD CACHE GROUP, UNLOAD CACHE GROUP, REFRESH CACHE GROUP or FLUSH CACHE GROUP statement may contain a subquery.

  • A WHERE clause in a LOAD CACHE GROUP, REFRESH CACHE GROUP or FLUSH CACHE GROUP statement can reference only the root table of the cache group, unless the WHERE 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 and owner.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;