Entering content frame

Background documentation Entries in the Column STRATEGY Locate the document in its SAP Library structure

The following table explains the possible entries in the column STRATEGY of the result table EXPLAIN.

Note

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
All columns of an index (and only these) are specified as a result of selected columns, after the keyword DISTINCT (DISTINCT specification (distinct_spec)), in any order. The system accesses the values for each index column only once. The system does not create a results table (such as
SELECT DISTINCT <all_columns_of_the_index> FROM ...).

DISTINCT OPTIMIZATION (P)

Partial Secondary Key
The first k (k < Total number of index columns) columns of an index are specified are specified in any order as a result of selected columns (<select_column>), after the key word DISTINCT. The system accesses the values for each index column only once. The system does not create a results table (such as
SELECT DISTINCT <first_k_columns_of_the_index> FROM ...).

DISTINCT OPTIMIZATION (K)

Primary Key
All columns of an index, and the first k (k <= total number of columns in the key) columns of the key are specified in any order as a result of selected columns (<select_column>), after the keyword DISTINCT. The system accesses the values for the corresponding index and key columns only once. The system does not create a results table (such as
SELECT DISTINCT <all_columns_of_the_index_+_first_k_columns_of_the_key> FROM ...).

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.

 

 

 

Leaving content frame