的mysql>select * from products;
GROUP BY显示了所有不同的列
+---------+-------------+-----------+------+
| prod_id | prod_source | prod_type | flag |
+---------+-------------+-----------+------+
| 1 | USA | 2 | 0 |
| 2 | USA | 2 | 0 |
| 3 | USA | 2 | 0 |
| 4 | USA | 3 | 1 |
| 5 | USA | 3 | 0 |
| 6 | BRA | 1 | 1 |
| 7 | BRA | 2 | 1 |
+---------+-------------+-----------+------+
所需resulset:
+-----------+----------+
| prod_type | count(*) |
+-----------+----------+
| 2 | 3 |
| 3 | 0 |
| 4 | 0 |
+-----------+----------+
where condition
prod_source = USA
flag=0
但我得到的结果集是
+-----------+----------+
| prod_type | count(*) |
+-----------+----------+
| 2 | 3 |
+-----------+----------+
与查询
SELECT prod_type ,count(*)
FROM products
WHERE prod_source='USA' and flag=0
GROUP by prod_type
ORDER by prod_type;
如何获得所有prod_type在美国的计数resulset?即使计数为0,它也必须在美国显示所有prod_type。
表定义:
CREATE TABLE `products` (
`prod_id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
`prod_source` VARCHAR(45) NOT NULL,
`prod_type` INTEGER UNSIGNED NOT NULL,
`flag` INTEGER UNSIGNED NOT NULL,
PRIMARY KEY (`prod_id`)
)
ENGINE = InnoDB;
数据插入:
INSERT INTO `products`
VALUES (1,'USA',2,0),
(2,'USA',2,0),
(3,'USA',2,0),
(4,'USA',3,1),
(5,'USA',4,1),
(6,'BRA',1,1),
(7,'BRA',2,1);
它在mysql中也工作正常。在select查询中,使用prod_type而不是prod_id。像这样使用 SELECT prod_type,SUM(CASE WHEN flag = 0 THEN 1 ELSE 0 END) FROM products WHERE prod_source ='USA' GROUP by prod_type ORDER by prod_type – Karthik 2010-08-16 07:25:36