The am_rescan purpose function
The database server typically calls am_rescan to process a join or subquery that requires multiple scans on the same table.
Syntax
mi_integer am_rescan(MI_AM_SCAN_DESC *scanDesc)- scanDesc
- Points to the scan descriptor.
Usage
Although am_rescan is an optional purpose function, the access method can enhance efficiency by supplying am_rescan for applications that involve joins, subqueries, and other multiple-pass scan processes. The am_rescan purpose function ends the previous scan in an appropriate manner and begins a new scan on the same open table.
Without an am_rescan purpose
function, the database server calls the am_endscan function
and then am_beginscan, if the access method provides
these functions.
Tip: To determine if an outer join might
cause a constant value to change, call mi_qual_const_depends_outer().
To determine the need to re-evaluate the qualification descriptor,
call mi_scan_newquals() from am_rescan.
Return values
- MI_OK
- Indicates success.
- MI_ERROR
- Indicates failure.