產生測驗資料：
CREATE TABLE `myquote` (
`id` int(8) unsigned NOT NULL AUTO_INCREMENT,
`code` text COLLATE utf8mb4_unicode_ci,
`date` date DEFAULT NULL,
`open` double DEFAULT NULL,
PRIMARY KEY (`id`)
) ;
INSERT INTO myquote(`code`, `date`, `open`)
VALUES ('a', '2020-01-01',10),
('a', '2021-01-01',20),
('a', '2022-01-01',30);
用group by分組后，select
select code,date,open from myquote group by code;
+------+------------+------+
| code | date | open |
+------+------------+------+
| a | 2020-01-01 | 10 |
+------+------------+------+
1 row in set (0.00 sec)
為何結果不是
+----+------+------------+------+
| id | code | date | open |
+----+------+------------+------+
| 1 | a | 2020-01-01 | 10 |
| 2 | a | 2021-01-01 | 20 |
| 3 | a | 2022-01-01 | 30 |
+----+------+------------+------+
3 rows in set (0.00 sec)
其他兩條也滿足情況哈，請談深入一點，謝謝。
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標籤：MySQL