Select is not using the Index

Question

Hi,
I have a Z-Table. The Primary key is:
EQUNR and LFDNR
I created now a new index with the field: EQUNR BSTNK .
Now I entered 3 equnrs and bstnk like 07* in SE16n
Normally what I thought should happen is that it uses the index to read the three equipments and than checks the field bstnk.
Instead it does a sequentiel read of the hole table that contains 12mio entries!
When I enter the bstnk more qualified like 0712354* the search is fast (1sec). Why is SAP bypassing the index and does a sequentiel read instead?!

Answer 1

Hi I checked,
ST05 the fast run was using an Index, the second didn't!
Thanks to  John. After I started a runstat on this table it worked.
But  the weird thing is when I use a inner join between my Z-Table and the EQUI table it doesn't use the index.
When I first select all equnrs in EQUI and then select the data from my z-Table with for all entries it uses my new index!
Example:
EQUNR has Index on field SERNR
Z-Table has Index on EQUNR + BSTNK
in sernrs I have ~5 full qualified sernos
in bstnk I have something like 07*
3 of these serialnumbers are in a bstnk that begins with 07.
          select *
            into corresponding fields of table search_result
            from equi as a
            inner join z-table as b on b~equnr = a~equnr
            where   a~sernr     in sernrs
              and   b~bstnk     in bstnks
After 5 min I have to kill the process. in SM50 I can see sequential read...
When I do this:
        select equnr
          from equi
          into corresponding fields of table lt_search_result
          where sernr in sernrs.
          select *
            from z_table
            into corresponding fields of table lt_search_result
            for all entries in lt_search_result
            where equnr = lt_search_result-equnr
              and bstnk in bstnks.
It takes 2sec and I got the result.
Edited by: Daniel Winter on Apr 21, 2010 8:51 AM
Edited by: Daniel Winter on Apr 21, 2010 8:51 AM