DB2 11 - Question on Index matching

Ravikumar sri2001

DB2 11 - Question on Index matching
Experts,
 
I have below query.
 
SELECT X_AMT FROM MY_TAB
WHERE  COL_A = WS-COL-A           AND
       DATE(COL_B_TMS) = WS-COL-B AND
       COL_C = 'PRSRT '           AND
       COLC_D = WS-COL-D
 
Index MY_IX is defined on the MY_TAB table as follows
 
COL_A CHAR(10)
COL_B TIMESTAMP
COL_C CHAR(8)
COL_D CHAR(8)
 
Host variables are defined as follows
 
WS-COL-A    PIC X(10)
WS-COL-B    PIC X(26)
WS-COL-D   PIC X(08)
  
As per the PLAN_TABLE, MATCOLS is "2" for the above query. Can you please explain why it is not using the predicates on COL_C, COL_D for index matching ?
 
Note : We are using Db2 11
 
Thanks,
Ravikumar