Locating Purpose Functions

The SQL statements that register a purpose function and an access method create records in the system catalog, which the database server consults to locate a purpose function.

As the access-method developer, you write the purpose functions and register them with the CREATE FUNCTION statement. When you register a purpose function, the database server puts a description of it in the sysprocedures system catalog table.

For example, assume you write a get_next_record() function that performs the tasks of the am_getnext purpose function. Assume that as user informix, you register the get_next_record() function. Depending on the operating system, you use one of the following statements to register the function:

CREATE FUNCTION get_next_record(pointer,pointer,pointer)
RETURNS int
WITH (NOT VARIANT)
EXTERNAL NAME "$INFORMIXDIR/extend/am_lib.bld(get_next_record)"
LANGUAGE C

CREATE FUNCTION get_next_record (pointer,pointer,pointer)
RETURNS int
WITH (NOT VARIANT)
EXTERNAL NAME "%INFORMIXDIR%\extend\am_lib.bld(get_next_record)"
LANGUAGE C

The get_next_record() declaration has three generic pointer arguments to conform with the prototype of the am_getnext purpose function. For a detailed explanation of the arguments and return value, refer to the description of am_getnext on page am_getnext.

As a result of the CREATE FUNCTION statement, the sysprocedures system catalog table includes an entry with values that are similar to the example in Table 5.

get_next_record 

informix 

163 

3 

pointer,pointer,pointer 

You then register the access method with a CREATE PRIMARY ACCESS_METHOD statement to inform the database server what function from sysprocedures to execute for each purpose.

The following example registers the super_access access method and identifies get_next_record() as the am_getnext purpose function.

CREATE PRIMARY ACCESS_METHOD super_access
(AM_GETNEXT = get_next_record) 

The super_access access method provides only one purpose function. If user informix executes the CREATE PRIMARY ACCESS_METHOD, the sysams system catalog table has an entry similar to Table 6.

super_access 

informix 

P

A