-- 为课程表添加学员统计等字段

ALTER TABLE `courses`
ADD COLUMN `student_count` INT DEFAULT 0 COMMENT '学习人数' AFTER `is_featured`,
ADD COLUMN `is_new` BOOLEAN DEFAULT TRUE COMMENT '是否新课程（最近30天内发布）' AFTER `student_count`,
ADD INDEX `idx_student_count` (`student_count`),
ADD INDEX `idx_is_new` (`is_new`);