1. ORACLE内部操作
   当执行查询时,ORACLE采用了内部的操作. 下表显示了几种重要的内部操作.

ORACLE Clause

内部操作 ORDER BY SORT ORDER BY

UNION

UNION-ALL

MINUS

MINUS

INTERSECT

INTERSECT

DISTINCT,MINUS,INTERSECT,UNION

SORT UNIQUE

MIN,MAX,COUNT

SORT AGGREGATE

GROUP BY

SORT GROUP BY

ROWNUM

COUNT or COUNT STOPKEY

Queries involving Joins

SORT JOIN,MERGE JOIN,NESTED LOOPS

CONNECT BY

CONNECT BY