Question

有没有办法实现这个目标？一个查询，可以从另一个表中的字段获取表名，并将该表的所有列压缩为一行键：val;对。（只有一个从关联表ft_data_id确定）

ID  FT_ID   FT_DATA_ID  NAME        TABLE                   DATA
1   1       1           one         features_data_one       ro_one: A; ro_two: B
2   2       1           two         features_data_two       rt_two: C; rt_two: D



/****** list of features with the name and the table the data lies in */
CREATE TABLE features (
        id INT AUTO_INCREMENT PRIMARY KEY,
        name VARCHAR(20) NOT NULL,
        `table` VARCHAR(255) NOT NULL
);
INSERT INTO features(name, `table`) VALUES ('one', 'features_data_one');
INSERT INTO features(name, `table`) VALUES ('two', 'features_data_two');


/****** feature one */
CREATE TABLE features_data_one (
        id INT AUTO_INCREMENT PRIMARY KEY,
        ro_one VARCHAR(20) NOT NULL,
        ro_two VARCHAR(20) NOT NULL
);
INSERT INTO features_data_one (ro_one, ro_two) VALUES ('A', 'B');



/****** feature two */
CREATE TABLE features_data_two (
        id INT AUTO_INCREMENT PRIMARY KEY,
        rt_one VARCHAR(20) NOT NULL,
        rt_two VARCHAR(20) NOT NULL
);
INSERT INTO features_data_two (rt_one, rt_two) VALUES ('C', 'D');

/****** association table which links a feature with a feature_id. The feature_id is the id in a specific table. This table is specificed in the feature table. */
CREATE TABLE assoc (
        id INT AUTO_INCREMENT PRIMARY KEY,
        ft_id INT NOT NULL,
        ft_data_id INT NOT NULL
);
INSERT INTO assoc (ft_id, ft_data_id) VALUES (1, 1);
INSERT INTO assoc (ft_id, ft_data_id) VALUES (2, 1);


SELECT * 
FROM assoc a
INNER JOIN features as ft ON a.ft_id = ft.id;

Answer 1

Imho，你正试图让SQL变得奇怪而且非常不自然。

为什么不尝试创建唯一的单个表？

CREATE TABLE features_all ( id INT AUTO_INCREMENT PRIMARY KEY, feature_name varchar(20) not null, ro_one VARCHAR(20) NOT NULL, ro_two VARCHAR(20) NOT NULL, index(feature_name) ); INSERT INTO features_all (feature_name, ro_one, ro_two) values ('one', 'A', '1'), ('one', 'C', '31'), ('one', 'Z', '71'), ('two', 'A', '1'), ('two', 'S', '12'), ('two', 'D', '14');

此样式有助于填充功能（添加第三个功能等）。只需插入新行！无需创建表格！

我不知道你的情况，但有时替换
很有用
index(feature_name)

带

unique(feature_name, ro_one)

确保您获得所选功能中任何键的唯一值

查询表以从字段中获取其他表的名称以执行最终查询

1 个答案: