1. Column O (Only Index)
'*' - The strategy only uses the specified single-column or multiple-column index for command processing. The data of the base table is not accessed. It is required that only columns contained in the index structure are accessed in the sequence of < select column>s or <where clause>, if any. Column names must be specified explicitly in the sequence of <select column>s (no SELECT * FROM ...).
2. Column D (Distinct Optimization)
- Column D only has an entry when column O contains an '*'.
'C' - (Complete Secondary Key)
In the sequence of <select column>s, all columns of a single-column or multiple-column index (and only those !) have been specified in any order after the keyword DISTINCT. Each time the values of the corresponding index columns are accessed only once. A result table is not built (e.g., SELECT DISTINCT <all columns of the index> FROM ...).
'P' - (Partial Secondary Key)
In the sequence of <select column>s, the first k (k < total number of columns in the index) columns of a multiple-column index have been specified in any order after the keyword DISTINCT. Each time, the values of the corresponding index columns are accessed only once. A result table is not built (e.g., SELECT DISTINCT <first k columns of the multiple-column index> FROM ...).
'K' - (Primary Key)
In the sequence of <select column>s, all columns of a single-column or multiple-column index and the first k (k <= total number of columns in the key) columns have been specified in any order after the keyword DISTINCT. Each time, the values of the corresponding index and key columns are accessed only once. A result table is not built (e.g., SELECT DISTINCT <all columns of the index + the first k columns of the key> FROM ...).
3. Column T (Temporary Index)
'*' - An internal temporary index is built. In this index, the keys of the hit rows are sorted in ascending order. The hit rows have been determined by the corresponding key columns. The base table is accessed via this temporary index.
4. Column M (More Qualifications)
'*' - On index or key columns, there are conditions which cannot be used to directly restrict the range for an access via index (e.g., in case of an EQUAL/IN condition on the first and third column of a multiple-colun index, only the first condition in the strategy will be used for access). Those conditions affect the corresponding index strategy. They are only used to restrict access to the base table.