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CBO and Missing Stats
When optimizer goal = CHOOSE
And statistics exists for 1 or more tables in join
And table has no statistics
CBO uses default statistics
Poor execution plan selection is very likely
Notes:
Caution: When CBO is in effect and statistics exist for one table in a join, but not another, Oracle will use default statistics for the table that does not have statistics. Poor plan selection is a likely result. Create statistics for all tables! If CHOOSE is the optimizer goal and statistics exist for just one table in the join but not the others, CBO will be turned on…