SQL/MP Reference Manual

HP NonStop SQL/MP Reference Manual—523352-013
U-5
Considerations—UPDATE

The optimizer chooses the alternate index as the access path.

The index columns in the equal-predicate are not changed by the update.

Another index column of the same index is updated to a higher value (if the
column is stored in ASCENDING order, or a lower value if the column is stored
in DESCENDING order).

For a fixed-length character column, an update value shorter than the column
length is padded with single-byte ASCII blanks (HEX20) to fill the column.
For a varying-length character column, an update value is not padded; its length is
the length of the value specified. In an entry-sequenced table, a value that updates
a varying-length character column must be the same length as the value it
replaces.

For information on buffering UPDATE operations, see CONTROL TABLE Directive
on page C-77.

These guidelines apply specifically to using the UPDATE statement in host
programs:

A TMF transaction must be in progress if you use the WHERE CURRENT OF
clause to update an audited table or view. The same TMF transaction must
include the OPEN cursor, FETCH, and UPDATE operations.

When using an SQL cursor in a host language program, an UPDATE WHERE
CURRENT operation provides a performance benefit over a stand-alone
UPDATE operation. Updating through a cursor uses virtual sequential block
buffering (VSBB) unless another cursor or a stand-alone UPDATE or DELETE
operation for the same table is used within the same process.
Use an UPDATE WHERE CURRENT operation instead of a stand-alone
operation to access a table (directly or through a view) within the same process
whenever possible. Using a stand-alone operation or another cursor to access
a table (directly or through a view) within the same process invalidates VSBB.
Invalidating VSBB can degrade performance substantially.

SQL returns these values to the SQLCODE variable after a DELETE:
The SQLCA records the number of rows updated.
0 The UPDATE succeeded
100 No rows satisfied the search condition
> 0 A warning was issued
< 0 An error occurred; the UPDATE did not complete