Why my table is not using Index?

I cant see my table is using Index...EXPLAIN given me this

id select_type  table      type  possible_keys  key key_len  ref   ro开发者_运维技巧ws Extra
1  SIMPLE           table1     const  web       web  258     const  1    
1  SIMPLE           table2     const  web       web  258     const  1    
1  SIMPLE           table3     const  web       web  258     const  1    
1  SIMPLE           table4     const  web       web  258     const  1   

It is using the index called web. Key means index.

id select_type      table      type   possible_keys  key  key_len  ref    rows Extra
1  SIMPLE           table1     const  web            web  258      const  1    
1  SIMPLE           table2     const  web            web  258      const  1    
1  SIMPLE           table3     const  web            web  258      const  1    
1  SIMPLE           table4     const  web            web  258      const  1
                                                     ^^^