使用约束来给mysql表添加字段和设置默认值。具体的操作方法如下:
1、首先新建一个学生表:student,需求:字段password的默认值是1213142。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/f11f3a292df5e0fe922ac1604c6034a85edf72a4?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
2、正常插入值,需要手动添加密码,但是如果有大量的字段可以使用默认值,那么语句会显得有点臃肿。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/3b292df5e0fe9925b03e213124a85edf8db171a4?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
3、现在设置字段password默认值,如图所示,实际上是创建了一个约束,所以图中的 df_pwd_stu 表示的是约束的名称,这时自定义的。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/95eef01f3a292df5eaf1e474ac315c6034a873a4?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
4、再次插入,这时可以忽略已经设置默认值字段的值了,因为插入的时候回数据库会帮插入默认值。完成效果图。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/2cf5e0fe9925bc31516f49f94edf8db1cb1370a4?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)