拿WordPress的数据库做一个对比
SELECT ID,post_title, post_author FROM wp_posts ORDER BY ID LIMIT 100;
OK, Time: 0.023000s
SELECT * FROM wp_posts ORDER BY ID LIMIT 100;
OK, Time: 0.261000s
SELECT `ID` , `post_author` , `post_date` , `post_date_gmt` , `post_content` , `post_title` , `post_excerpt` , `post_status` , `comment_status` , `ping_status` , `post_password`, `post_name` , `to_ping` , `pinged` , `post_modified` , `post_modified_gmt`, `post_content_filtered`, `post_parent` , `guid`, `menu_order`, `post_type`, `post_mime_type`, `comment_count` FROM wp_posts ORDER BY ID LIMIT 100;
OK, Time: 0.231000s
总结
- 字段更少速度更快
- 没有大内容字段查询速度更快,有大内容字段的表需要最优速度时,可以写明 select 的字段来排除大内容字段
- select * 和 select 全部字段的查询速度相差不大,为了便于开发,可以用 select *,需求变更时少改些地方