简短回答：
考虑到所描述的两个表：

insert into A (select 5, sub_category_id, category_id, false from B where category_id = 1);

详细说明：
a内容：

select * from A;
+---------+-----------------+-------------+------------+
| user_id | sub_category_id | category_id | is_removed |
+---------+-----------------+-------------+------------+
|       5 |             201 |           2 |          0 |
+---------+-----------------+-------------+------------+

b内容：

select * from B;
+-----------------+-------------+
| sub_category_id | category_id |
+-----------------+-------------+
|             101 |           1 |
|             102 |           1 |
|             103 |           1 |
|             201 |           2 |
+-----------------+-------------+

创建视图：

select 5, sub_category_id, category_id, false from B where category_id = 1;
+---+-----------------+-------------+-------+
| 5 | sub_category_id | category_id | FALSE |
+---+-----------------+-------------+-------+
| 5 |             101 |           1 |     0 |
| 5 |             102 |           1 |     0 |
| 5 |             103 |           1 |     0 |
+---+-----------------+-------------+-------+

插入：

insert into A (select 5, sub_category_id, category_id, false from B where category_id = 1);
+---------+-----------------+-------------+------------+
| user_id | sub_category_id | category_id | is_removed |
+---------+-----------------+-------------+------------+
|       5 |             201 |           2 |          0 |
|       5 |             101 |           1 |          0 |
|       5 |             102 |           1 |          0 |
|       5 |             103 |           1 |          0 |
+---------+-----------------+-------------+------------+