Registering the Access Method

The CREATE FUNCTION statement identifies a function as part of a database, but not necessarily as part of an access method. To register the access method, issue the CREATE PRIMARY ACCESS_METHOD statement, which sets values in the sysams system catalog table, such as:

• The unique name of each purpose function
• A storage-type (extspaces or sbspaces) indicator
• Flags that activate optional features, such as writable data or clustering

The sample statement in Figure 2 assigns registered function names to some purpose functions. It specifies that the access method should use sbspaces and it enables clustering.

CREATE PRIMARY ACCESS_METHOD my_virtual
(  AM_OPEN = open_virtual,
   AM_CLOSE = close_virtual,
   AM_CREATE = create_virtual,
   AM_DROP = drop_virtual,
   AM_BEGINSCAN = beginscan_virtual,
   AM_GETNEXT = getnext_virtual,
   AM_ENDSCAN = endscan_virtual,
   AM_INSERT = insert_virtual,
   AM_DELETE = delete_virtual,
   AM_UPDATE = update_virtual,
   AM_READWRITE,
   AM_ROWIDS,
   AM_SPTYPE = S,
   AM_CLUSTER)

Figure 3 shows the resulting sysams system catalog entry for the new access method.

am_name        my_virtual
am_owner       informix
am_id          101
am_type        P
am_sptype      S
am_cluster     1
am_rowids      1
am_readwrite    1
am_parallel    0
am_costfactor  1.000000000000
am_create      162
am_drop        163
am_open        164
am_close       165
am_insert      166
am_delete      167
am_update      168
am_stats       0
am_scancost    0
am_check       0
am_beginscan   169
am_endscan     170
am_rescan      0
am_getnext     171

The statement in Figure 2 does not name a purpose function for am_stats, am_scancost, or am_check, as the 0 values in Figure 3 indicate. The database server sets a 0 value for am_parallel because none of the CREATE FUNCTION statements for the purpose functions included the PARALLELIZATION routine modifier.

For syntax and a list of available purpose settings, refer to SQL Statements for Access Methods.