在一个100多万行记录的表上的char(1)列C上做了个索引runstats后测试了一下各个语句是否走索引结果发现select * from tabname where C='0' 不会走索引select * from tabname where C != '0' 会走索引用db2expln来看的我认为都应该走索引才对。。。 比较奇怪顺便问一下，例...显示全部
select count(*) from tabname where C='0' returns how many rows? select count(*) from tabname where C!='0' returns how many rows? if " C!='0'" contains ton of rows, there is no reason to do index scan The primary purpose of indexing is to help returning small portion of data.