MySQL支持降序索引：DESC在索引定義中不再被忽略，但會導致按鍵降序存儲鍵值。
而且只有InnoDB存儲引擎支持降序索引
例如：創建表
CREATE TABLE test.t (
id INT NOT NULL auto_increment PRIMARY KEY,c1 INT, c2 INT
);
插入數據
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優化器查看
EXPLAIN select FROM test.t WHERE c1=1 ORDER BY c1 ASC, c2 ASC;
創建索引排序
CREATE INDEX idx1 ON test.t(c1,c2);
使用sql優化器查看
EXPLAIN select FROM test.t WHERE c1=1 ORDER BY c1 ASC, c2 ASC;
使用sql優化器查看
EXPLAIN select FROM test.t WHERE c1=1 ORDER BY c1 ASC, c2 DESC;
創建索引排序
CREATE INDEX idx1 ON test.t(c1,c2);
使用sql優化器查看
EXPLAIN
SELECT FROM test.t ORDER BY c1 ASC,c2 DESC;
查看錶結構
SHOW CREATE TABLE t;
