Update in order by

Question

Table 1

DataValue    TokenIndex
AB                  NULL

TABLE 2


TokenIndex    TokenValue
1                    AB
2                  ABAC


i want to update my table1 (TokenIndex) with the  (TokenIndex)  of table2  where table1 (DataValue) (sql LIKE) with (TokenValue)  
TABLE 2   with longest string

EG. AB like like   AB,and ABAC also  but i want 'ABAC'  TokenIndex (which is 2)    to update  in Token index of Table 1  against AB


i want retult 

Table 1

DataValue    TokenIndex
AB                  2