MYSQL: How to select every 4th row STARTING from 3rd row?

Question

meaning the result should be selecting 3rd, 7th, 11th, 15 rows etc. Every row has an ID, in ascending order. I am stuck on this for hours! Any help is highly appreciated!

Answer 1

Suppose your schema is:

   CREATE TABLE t1 (
      id int(11) DEFAULT NULL,
      data varchar(20) DEFAULT NULL
    );

mysql> select * from t1;
+------+--------+
| id   | data   |
+------+--------+
|    1 | abc-1  |
|    2 | abc-2  |
|    3 | abc-3  |
|    4 | abc-4  |
|    5 | abc-5  |
|    6 | abc-6  |
|    7 | abc-7  |
|    8 | abc-8  |
|    9 | abc-9  |
|   10 | abc-10 |
|   11 | abc-11 |
|   12 | abc-12 |
|   13 | abc-13 |
|   14 | abc-14 |
|   15 | abc-15 |
|   16 | abc-16 |
+------+--------+
16 rows in set (0.00 sec)

mysql> select id,data from  (select mod(@r:=@r+1,4) as isfetch,id,data from t1,(select @r:=0) s) k where k.isfetch=0 order by id;
+------+--------+
| id   | data   |
+------+--------+
|    4 | abc-4  |
|    8 | abc-8  |
|   12 | abc-12 |
|   16 | abc-16 |
+------+--------+
4 rows in set (0.01 sec)

Answer 2

一种更简单的方法是在 id 本身上使用 mod：

select * from table where (id + 1) mod 4 = 0;