排序数据

ORDER BY

//普通排序
SELECT table_name FROM innodb_table_stats;
// 加了ORDER BY子句  以字母顺序排序数据 
SELECT table_name FROM innodb_table_stats ORDER BY table_name;

按多个列排序

//检索这三个  让 parent_category_id, name 顺序排列 先排parent_category_id有相同parent_category_id才会  //对name进行排列 如果parent_category_id 都是唯一则不会按name排序
SELECT parent_category_id, name, help_category_id FROM help_category ORDER BY parent_category_id, name;

指定排序方向

进行降序排序， 必须指定DESC关键字

SELECT parent_category_id, name, help_category_id FROM help_category ORDER BY parent_category_id DESC;
//默认升序 关键字ASC

DESC关键字只应用到直接位于其前面的列名,name还是升序排列

SELECT parent_category_id, name, help_category_id FROM help_category ORDER BY parent_category_id DESC, name;

使用ORDER BY和LIMIT的组合，能够找出一个列中最高或最低的值。

//parent_category_id 的最大值
SELECT parent_category_id, name, help_category_id FROM help_category ORDER BY parent_category_id DESC LIMIT 1;