example.对字段进行去重
$index = $select->distinct ( true )->where ( 'parent_id=0' )->field ( 'index' )->select ();
SELECT TOP 3
degree ,
COUNT(1) AS 人数
FROM
Student
GROUP BY
degree
ORDER BY
degree DESC
example.对字段进行去重
$index = $select->distinct ( true )->where ( 'parent_id=0' )->field ( 'index' )->select ();
数据库字段唯一约束吧