多选题Which three statements are true about SQL plan directives?（）AThey are tied to a specific statement or SQL id.BThey instruct the maintenance job to collect missing statistics or perform dynamic sampling to generate a more optimal plan.CThey are used to
题目
多选题
Which three statements are true about SQL plan directives?（）
A
They are tied to a specific statement or SQL id.
B
They instruct the maintenance job to collect missing statistics or perform dynamic sampling to generate a more optimal plan.
C
They are used to gather only missing statistics.
D
They are created for a query expression where statistics are missing or the cardinality estimates by the optimizer are incorrect.
E
They instruct the optimizer to create only column group statistics.
F
Improve plan accuracy by persisting both compilation and execution statistics in the SYSAUX tablespace.