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The optimizer could not find a unique index which it could use to scan table '%.*s' for cursor '%.*s'.
For an explicit updated cursor scan, Adaptive Server requires that a unique index exist on the table. A unique index ensures that the cursor is positioned at the correct row the next time a fetch is performed on that cursor. Error 311 occurs when a unique index does not exist during a scan required for a cursor marked for update.
Create a unique index using the following methods:
Drop your existing index. Create an index with the unique option or use alter table add constraint with the unique option.
Create a new index using create index with the unique option or use alter table add constraint with the unique option.
When you create an index with the unique option,
if there is a duplicate key value or if more than one row contains
a null value, the command is aborted and error 1505 is raised, showing
the duplicate value. See to “Error 1505” if that happens.
Add an IDENTITY column using alter table and the identity option.
If your table has one or more IDENTITY columns, you can, for future indexes you create for this table, use the database option identity in nonunique index. When this option is set, any nonunique index created on a table with an IDENTITY column will have the IDENTITY column automatically included as the last key field of the index. This allows an otherwise nonunique index to be used for a cursor marked for update.
However, all indexes would then be considered unique by the optimizer since every index that is created would be unique and this could result in poor performance for some queries. Since the identity in nonunique index option does not affect existing indexes, only future indexes you create, the existing 311 error will not be resolved.
WARNING! Do not use the identity in nonunique index option unless you plan to test your queries.
To use the identity in nonunique index option, the table must already have an IDENTITY column, either from a create table statement or by setting the auto identity database option to true before creating the table.
The commands to set this option are:
1> use master 2> go 1> sp_dboption <database_name>, 2> "identity in nonunique index", true 3> go
1> use <database_name> 2> go 1> checkpoint 2> go
Refer to the Reference Manual: Commands for information about create index and alter table, and Reference Manual: Procedures for information about sp_dboption.
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