Thanks to Yuhao,

Is the column M.C1 ignored when I invoke " create index idx on EXAMPLE (M.C0, M.C1) " ? 

Which of the following two solutions make sense?

solution a):
     create index idx_1 on EXAMPLE (M.C0, M.C1)
     create index idx_2 on EXAMPLE (M.C1, M.C0)


solution b):
    create index idx_1 on EXAMPLE (M.C0)
    create index idx_2 on EXAMPLE (M.C1)




2015-05-17 22:34 GMT+08:00 Yuhao Bi <byh0831@gmail.com>:
Hi Xiao Tao,

You can create another secondary index on the same columns.
    create index another_index on EXAMPLE(M.C1, M.C0)

After doing that, query b) should return faster.

2015-05-17 22:25 GMT+08:00 Tao Xiao <xiaotao.cs.nju@gmail.com>:
I tried to build secondary index for two columns, M.C0 and M.C1:  

      create index my_idx on EXAMPLE (M.C0, M.C1)


Then I tried to query by two indexes, respectively:

    a). select M.C0 from EXAMPLE where M.C0 = 'c0_00000001'
    b). select M.C1 from EXAMPLE where M.C1 = 'c1_00000001'

Query a) returned results in less than 0.3 second, and query b) returned results in about 13 seconds. It seems that index was built for column M.C0, not M.C1

Can we build secondary index for two or more columns ? 

Thanks.