MySQL每隔两列获取前3行
我试图在mysql中实现以下目标: 我有一个包含以下数据的表格:MySQL每隔两列获取前3行,mysql,sql,greatest-n-per-group,window-functions,Mysql,Sql,Greatest N Per Group,Window Functions,我试图在mysql中实现以下目标: 我有一个包含以下数据的表格: DROP TABLE IF EXISTS my_table; CREATE TABLE my_table (a CHAR(1) NOT NULL ,b CHAR(1) NOT NULL ,factor INT NOT NULL ,PRIMARY KEY(a,b,factor) ); INSERT INTO my_table VALUES ('A','X',90), -- should be included ('A','X',
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(a CHAR(1) NOT NULL
,b CHAR(1) NOT NULL
,factor INT NOT NULL
,PRIMARY KEY(a,b,factor)
);
INSERT INTO my_table VALUES
('A','X',90), -- should be included
('A','X',80), -- should be included
('A','X',70), -- should be included
('A','X',60), -- should NOT be included
('A','Y',70), -- should be included
('A','Y',60), -- should be included
('A','Y',50), -- should be included
('A','Y',40); -- should NOT be included
我希望我的查询在列A和列b的组合中每前三行返回一次。因此,最高的3行因子将保持不变
+---+---+--------+
| a | b | factor |
+---+---+--------+
| A | X | 90 |
| A | X | 80 |
| A | X | 70 |
| A | Y | 70 |
| A | Y | 60 |
| A | Y | 50 |
+---+---+--------+
我已经找到了解决方案,但这一个只适用于一列,而不是两列
有什么想法吗?选择cte*,
按列a、列b分区的行数
按系数顺序描述
从桌子上
选择列a、列b、系数
来自cte
其中rn对于MySQL 8.0之前的版本
SELECT x.*
FROM my_table x
JOIN my_table y
ON y.a = x.a
AND y.b = x.b
AND y.factor >= x.factor
GROUP
BY x.a
, x.b
, x.factor
HAVING COUNT(*) <= 3
ORDER
BY a
, b
, factor DESC;
…关于下一次,请参见:行是如何排序的?如何确定行是第一行、第二行?记住-顺序不安全。嗨,第一顺序=列a ASC,列b ASC,因子描述