多项选择题

Which two are true regarding external tables？ （）

A.External tables can be updated. 
B.External tables are read-only tables. 
C.Indexes can be created on external tables. 
D.Indexes cannot be created on external tables.

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单项选择题
Consider the following statement：   SQL> EXECUTE DBMS_STATS.GATHER_SHEMA_STATS （-  2> ownname => ‘OE’， -  3> estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE， -  4> method opt => ‘for all columns size AUTO’）；   What is the effect of ‘for all columns size AUTO’ of the METHOD_OPT option？（）

A.The Oracle server creates a new histogram based on existing histogram definitions for all table, column, and index statistics for the OE schema. 
B.The Oracle server creates a histogram based on data distribution regardless of how the application uses the column/s for all table, column, and index statistics for the OE schema.
C.The Oracle server creates a histogram based on data and application usage of the column/s for all table, column, and index statistics for the OE schema. 
D.The Oracle server creates a histogram based on application usage, regardless of data distribution, for all table, column, and index statistics for the OE schema.
多项选择题
Examine the list of variables and their data types：  AME DATA Type  TS， TS1 TIMESTAMP  TSZ TIMESTAMP WITH TIME ZONE  TLZ TIMESTAMP WITH LOCAL TIME ZONE  IYM INTERVAL YEAR TO MONTH  IDS， IDSI INTERVAL YEAR To SECOND   Which three expressions using the new data and time data types are valid？（）

A.IDS* 2
B.TS + IYM
C.TS –TSI
D.IDS – TS
E.IDS + IYM
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