Solution for using Filesort for MySQL order by

http://blog.csdn.net/yangyu112654374/article/details/4251624

such as an SQL statement

SELECT * from TABLE1 where a1=1 and a2=2 and a3=3 order by A4 ASC;

After optimization: Select A4,a1,a2 ... From TABLE1 where A1=1 and a2=2 and a3=3 order by A4 ASC; And index the A4,A1,A2,A3, when using order by A4, the Federated index should put A4 in the first place.

The order by field must appear when select is in line

2. From the above can be seen in the federated index, or can be called Multi-column index, such as key (' A1 ', ' A2 ', ' A3 ', ' A4 ') and so on, the sort of thinking is generally, first follow the A1 to sort, A1 the same, and then sort by A2, and so on (A1), (A1,A2) A2,A3) indexes are valid, but indexes such as (A2,A3) are not valid.

Solution for using Filesort for MySQL order by