READ TABLE ..... BINARY SEARCH问题

Read Table 的语法很多，这里说一种特殊情况，Read　Table 中查询的时候对标准内表经常有一种二分优化查找，用Binary
search的时候首先必须要有查询条件；但如果查询条件满足的项目不至一条时，这时得到的是这些数据中索引排在最前面的数据；

如： 001   0001   20100101

001   0001  20100103

001   
0001  20100105

READ TABLE itab  INTO  wa  WITH KEY  col1 = ‘001‘

                                     col2 = ‘0001‘

                                     BINARY SEARCH.


这时得到的是第一条，001 0001 20100101 而不是 001 0001
20100103   
这好像不符合二分法查找逻辑。按结果来看，这里的机制是先去匹配了查询条件，将匹配查询条件的数据全拉出来，然后取第一条，而不是按binary search
正常机制，先将low+high / 2位置的数据与条件匹配，成功就取出来。从结果来看，ABAP的二分机制实际是没用的。

然后做如下测试，先不对数据排序；

如： 001   0001   20100101

001  
0002  20100103

001   
0001  20100105

001   
0003  20100105

001   
0001  20100107

READ TABLE itab  INTO  wa  WITH KEY  col1 = ‘001‘

                                     col2 = ‘0001‘

                                     BINARY SEARCH.

得到的结果是001 
0001  20100101 也是索引最低数据；

所以最好的解释：ABAP的二分查找机制是按位置n/2,n/4、、、再一半、、、直到最后一条数据；在这个过程中得到匹配数据仍然不停止将继续二分查找，不断的用新的匹配数据去匹配旧的数据；因为新的数据索引肯定比旧的索引低；

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时间： 2024-10-16 21:31:26

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