# Composite Index (Continue...)

+ Overwrite index: When the data can be obtained completely through the index, TiDB can retrieve the data directly by traversing the index without returning the table, reducing I/O operations. Therefore, in real practical applications, overwriting indexes is one of the main optimizations to improve performance
```
select c1 from t2 where c1 = 1 and c2 = 10 and c3 between 1 and 200;
select c1, c2, c3 from t2 where c1 = 1 and c2 between 1 and 200;
```
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