Is there a oracle hint to execute the where clauses in a specific order?

Question

Consider the following two queries on a table where datecolumn is indexed -

Q1: select * from table where datecolumn > sysdate - 5;
Q2: select * from table where datecolumn > sysdate - 5 and datecolumn < sysdate - 1;

Q1 uses the index. But, Q2 somehow does a full table scan. Is it because oracle somehow chooses to execute "datecolumn < sysdate - 1" first ? In that case, is there a way to enforce order of execution of where clauses involving one column ?

Answer 1

You could specify an index hint, something like this:

select /*+ INDEX (table datecolumn_ix)*/ 
       * 
  from table 
  where datecolumn > sysdate - 5 and datecolumn < sysdate - 1;

See Oracle Index Hint for more details.

Answer 2

Sure there is the index hint.

/*+ INDEX(table index_name) */

But, in your case maybe is better to collect statistics of your table.

Use DBMS_STATS.GATHER_TABLE_STATS('schema','table') procedure.

Answer 3

Oracle doesn't guarantee by default that your tables will be joining in the same order as you mentioned, thus you may use these hints:

1. ordered https://docs.oracle.com/cd/B10500_01/server.920/a96533/hintsref.htm#5555 It will join your tables in the same order as you mentioned in where statement

2. leading https://docs.oracle.com/cd/B10500_01/server.920/a96533/hintsref.htm#5730 you may specify the join orders of your tables

   select /*+ leading (c b a) */
     a.*
   from
     tablea a
     , tableb b
     , tablec c
   where
     a.some_id = b.some_id
     and c.some_id = b.other_id
   

   Also, for your Q2 you may try the between option https://docs.oracle.com/cd/B28359_01/server.111/b28286/conditions011.htm