我用alter session set events '10046 trace name context forever,level 12' 跟踪一个查询:select * from emp_reg where empno=100表emp_reg在empno列有索引. 跟踪显示有如下三个I/O： WAIT #1: nam='db file sequential read' ela= 5725 p1=16 p2=1314 p3=1 WAIT #1: nam='db file sequential read' ela= 211 p1=16 p2=1315 p3=1 WAIT #1: nam='db file sequential read' ela= 199 p1=16 p2=1311 p3=1 p1,p2,p3分别为文件、块与读块个数。现在p1=16是对的，但p2=1314 1315 1311跟本和表所在的块不符。 使用show_space显示的表emp_reg的所在块： SQL> exec show_space('EMP_REG'); Free Blocks.............................0 Total Blocks............................768 Total Bytes.............................3145728 Unused Blocks...........................176 Unused Bytes............................720896 Last Used Ext FileId....................16 Last Used Ext BlockId...................1809 Last Used Block.........................80 这上empno列上的索引的所在块 SQL> exec show_space('PK_EMP_REG',user,'INDEX'); Free Blocks.............................0 Total Blocks............................224 Total Bytes.............................917504 Unused Blocks...........................10 Unused Bytes............................40960 Last Used Ext FileId....................16 Last Used Ext BlockId...................1521 Last Used Block.........................6 这是为什么啊？