MySQL支持降序索引：DESC在索引定义中不再被忽略，但会导致按键降序存储键值。

而且只有InnoDB存储引擎支持降序索引例如：创建表CREATE TABLE test.t (id INT NOT NULL auto_increment PRIMARY KEY,c1 INT, c2 INT);插入数据INSERT into test.t (c1,c2) VALUES (1,2),(1,3),(1,4),(4,2),(4,1),(4,3),(2,1),(2,3),(2,4),(3,2),(3,1),(3,4);使用sql优化器查看EXPLAIN select FROM test.t WHERE c1=1 ORDER BY c1 ASC, c2 ASC;

创建索引排序

CREATE INDEX idx1 ON test.t(c1,c2);

使用sql优化器查看

EXPLAIN select FROM test.t WHERE c1=1 ORDER BY c1 ASC, c2 ASC;使用sql优化器查看EXPLAIN select FROM test.t WHERE c1=1 ORDER BY c1 ASC, c2 DESC;

创建索引排序

CREATE INDEX idx1 ON test.t(c1,c2);

使用sql优化器查看

EXPLAIN

SELECT FROM test.t ORDER BY c1 ASC,c2 DESC;查看表结构SHOW CREATE TABLE t;