<number of> <optimizer_strategy_executes>, selectivity <percentage>%: <number of> rows read, <number of> rows qualified
The ratio of read table rows to found table rows is poor when a particular access strategy (<optimizer_strategy_executes>) is used.
The access strategy can be one of the following strategies:
·
Primary key accesses
(EQUAL CONDITION FOR
KEY COLUMN,
EQUAL
CONDITION FOR KEY COLUMN (SUBQ),
IN CONDITION
FOR KEY COLUMN)
·
Primary key range accesses
(RANGE
CONDITION FOR KEY COLUMN,
RANGE
CONDITION FOR KEY COLUMN (SUBQ),
IN CONDITION
FOR KEY COLUMN)
·
Index accesses
(EQUAL CONDITION FOR
INDEX,
EQUAL
CONDITION FOR INDEX (SUBQ),
IN CONDITION
FOR INDEX)
·
Index range accesses
(RANGE CONDITION FOR
INDEX,
RANGE
CONDITION FOR INDEX (SUBQ),
IN CONDITION
FOR INDEX)
·
Isolated index accesses
see: EXPLAIN Statement:
Columns O,D,T,M, column O (Only Index)
and Index accesses
·
Isolated index range accesses
see: EXPLAIN Statement:
Columns O,D,T,M, column O (Only Index)
and Index range accesses
·
Isolated index scans
(INDEX
SCAN)
Find the statement that causes this poor ratio of read rows to found rows, and check the access strategies for this statement.
For information on creating optimized SQL statements, see the SQL Optimizer documentation.
See also: Table scans