我知道MySQL中没有序列发生器。即使我想知道是否有一种方法可以实现:我有以下选择,需要在其中生成带有计数器的字段
mysql> select name, age, hobby, ' ' counter from t order by name;
+------------+------+--------------+---------+
| name | age | hobby | counter |
+------------+------+--------------+---------+
| Mark | 21 | Soccer | |
| Mark | 21 | Football | |
| pizzipizzi | 7 | cronchcronch | |
| Steve | 23 | Basketball | |
| Steve | 23 | Coding | |
| Steve | 23 | Soccer | |
+------------+------+--------------+---------+
5 rows in set (0.01 sec)
所需的结果集(每个新名称的计数器都重置为0:]
+------------+------+--------------+---------+
| name | age | hobby | counter |
+------------+------+--------------+---------+
| Mark | 21 | Soccer | 0 |
| Mark | 21 | Football | 1 |
| pizzipizzi | 7 | cronchcronch | 0 |
| Steve | 23 | Basketball | 0 |
| Steve | 23 | Coding | 1 |
| Steve | 23 | Soccer | 2 |
+------------+------+--------------+---------+
任何帮助将不胜感激。
请考虑以下内容:
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id SERIAL PRIMARY KEY
,name VARCHAR(20) NOT NULL
,age INT NOT NULL
,hobby VARCHAR(20) NOT NULL
);
INSERT INTO my_table (name,age,hobby) VALUES
('Mark',21,'Soccer'),
('Mark',21,'Football'),
('pizzipizzi',7,'cronchcronch'),
('Steve',23,'Basketball'),
('Steve',23,'Coding'),
('Steve',23,'Soccer');
SELECT x.*
, COUNT(y.id)-1 counter
FROM my_table x
JOIN my_table y
ON y.name = x.name
AND y.age = x.age
AND y.id <= x.id
GROUP
BY x.id;
+----+------------+-----+--------------+---------+
| id | name | age | hobby | counter |
+----+------------+-----+--------------+---------+
| 1 | Mark | 21 | Soccer | 0 |
| 2 | Mark | 21 | Football | 1 |
| 3 | pizzipizzi | 7 | cronchcronch | 0 |
| 4 | Steve | 23 | Basketball | 0 |
| 5 | Steve | 23 | Coding | 1 |
| 6 | Steve | 23 | Soccer | 2 |
+----+------------+-----+--------------+---------+
注意,在MySQL 8.0+中,您有更多选择