Hierarchy
SAP_BASIS (Software Component) SAP Basis Component⤷
BC-DB-DB4 (Application Component) DB2 for AS/400⤷
STU4 (Package) CCMS / AS/400
Basic Data
| Data Element | QQKS |
| Short Description | iSeries: Key Selection (Database Monitor) |
Data Type
| Category of Dictionary Type | D | Domain |
| Type of Object Referenced | No Information | |
| Domain / Name of Reference Type | QQYN | |
| Data Type | CHAR | Character String |
| Length | 1 | |
| Decimal Places | 0 | |
| Output Length | 1 | |
| Value Table |
Further Characteristics
| Search Help: Name | ||
| Search Help: Parameters | ||
| Parameter ID | ||
| Default Component name | ||
| Change document | ||
| No Input History | ||
| Basic direction is set to LTR | ||
| No BIDI Filtering |
Field Label
| Length | Field Label | |
| Short | 11 | Key Sel. |
| Medium | 21 | Key Selection |
| Long | 41 | Key Selection |
| Heading | 55 | Key Selection |
Documentation
Definition
QQKS indicates if the key selection access method was used to implement a statement.
Y = Key selection access method was used
N = Key selection access method was not used
In the case of the file-based monitor (STRDBMON/ENDDBMON), QQKS is available only for records with QQRID 3001 and 3002, QQILNM/QQILNM is the index used for key positioning.
In the case of the memory-resident database monitor, QQKS is only available in the detail information tables SQ3001_DB4 and SQ3002_DB4, QQILNM/QQILNM is the index used for key positioning.
Note
The key selection access method:
The entire index is read and any selection criteria that references the key fields of the index is applied against the index.
The advantage of this method is that the data space is only accessed to retrieve records that satisfy the selection criteria applied against the index. Any selection not performed through this key selection method is performed using dynamic processing at the dataspace level.
Example
Consider the query
select * from FILE
where f1 = 'a' and f3 = 'b' and f4 = 'c'
order by f1
where FILE is a table with the fields F1, F2, F3, F4, F5 - all of type CHAR(5) - and a unique index FILE_1 over the fields F1, F2, F3, F4 exists.
This query will be implemented using the existing index FILE_1.
Key positioning (see Note for QQKP) is performed only on the leftmost key field of the index (QQI3 = 1 for QQRID = 3001).
On all index entries that match the selection criteria for F1, key selection is now perfromed meaning that the remaining selection criteria (f3 = 'b' and f4 = 'c') is applied against these selected index entries.
History
| Last changed by/on | SAP | 20070813 |
| SAP Release Created in |
