是否可以像这样遍历一个表:
mysql> select * from `stackoverflow`.`Results`; +--------------+---------+-------------+--------+ | ID | TYPE | CRITERIA_ID | RESULT | +--------------+---------+-------------+--------+ | 1 | car | env | 1 | | 2 | car | gas | | | 3 | car | age | | | 4 | bike | env | 1 | | 5 | bike | gas | | | 6 | bike | age | 1 | | 7 | bus | env | 1 | | 8 | bus | gas | 1 | | 9 | bus | age | 1 | +--------------+---------+-------------+--------+ 9 rows in set (0.00 sec)
Into this:
+------+-----+-----+-----+ | TYPE | env | gas | age | +------+-----+-----+-----+ | car | 1 | | | | bike | 1 | | 1 | | bus | 1 | 1 | 1 | +------+-----+-----+-----+
The aim is to select all the CRITERIA_ID
s and use them as a column.
As rows i like to use all the TYPE
s .
- All Criterias:
SELECT distinct(CRITERIA_ID) FROM stackoverflow.Results;
- All Types
SELECT distinct(TYPE) FROM stackoverflow.Results;
But how combine them into a view or smth. like this?
If you like to play with the data. This is a script to generate the table:
CREATE SCHEMA `stackoverflow`;
CREATE TABLE `stackoverflow`.`Results` (
`ID` bigint(20) NOT NULL AUTO_INCREMENT,
`TYPE` varchar(50) NOT NULL,
`CRITERIA_ID` varchar(5) NOT NULL,
`RESULT` bit(1) NOT NULL,
PRIMARY KEY (`ID`)
)
ENGINE=InnoDB;
INSERT INTO `stackoverflow`.`Results`
(
`ID`,
`TYPE`,
`CRITERIA_ID`,
`RESULT`
)
VALUES
( 1, "car", env, true ),
( 2, "car", gas, false ),
( 3, "car", age, false ),
( 4, "bike", env, true ),
( 5, "bike", gas, false ),
( 6, "bike", age, true ),
( 7, "bus", env, true ),
( 8, "bus", gas, true ),
( 9, "bus", age, true );
最佳答案
不幸的是,MySQL 没有 PIVOT
函数,这基本上就是您要尝试做的。因此,您需要使用带有 CASE
语句的聚合函数:
SELECT type,
sum(case when criteria_id = 'env' then result end) env,
sum(case when criteria_id = 'gas' then result end) gas,
sum(case when criteria_id = 'age' then result end) age
FROM results
group by type
现在,如果您想动态地执行此操作,这意味着您事先不知道要转置的列,那么您应该查看以下文章:
Dynamic pivot tables (transform rows to columns)
您的代码如下所示:
SET @sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'SUM(IF(CRITERIA_ID = ''',
CRITERIA_ID,
''', RESULT, NULL)) AS ',
CRITERIA_ID
)
) INTO @sql
FROM
Results;
SET @sql = CONCAT('SELECT type, ', @sql, ' FROM Results GROUP BY type');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
关于mysql - 在mysql中选择动态列,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11899647/