The following table explains the possible entries in the column STRATEGY of the result table EXPLAIN.
For information on the structure of this result table, see the Reference Manual under EXPLAIN Statement.
Entry |
Meaning |
ONLY INDEX ACCESSED |
This strategy uses only the specified index to process the command. The system does not access the basis table data. To enable this, only columns that are contained in the index structure can be addressed in the sequence of selected columns or in a WHERE clause, if one exists. |
DISTINCT OPTIMIZATION (A) |
The complete key is in the SELECT list/output columns. This means that the result is automatically free from duplicates. |
DISTINCT OPTIMIZATION (C) |
Complete Secondary Key |
DISTINCT OPTIMIZATION (P) |
Partial Secondary Key |
DISTINCT OPTIMIZATION (K) |
Primary Key |
TEMPORARY INDEX CREATED |
A temporary index is created internally, in which the keys of the hit rows determined by the corresponding index columns are stored in ascending order. The system accesses the basis table using this temporary index. |
ADDNL. QUALIFICATION ON INDEX |
There are search conditions for index or key columns that cannot be used for the direct containment of the range for an index access (for example, in the case of an equality /IN condition, for the first and third columns of a multi-column index, only the first search condition of the search strategy is used for access). These search conditions influence the corresponding index strategy: they are used to restrict accesses to the basis table. |