我有4个表:SQL与动态字段
CREATE TABLE Category (
Id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
Name VARCHAR(255) NOT NULL,
) Engine=InnoDB;
CREATE TABLE Category_Template (
Id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
Name VARCHAR(255) NOT NULL,
Category_Id INT UNSIGNED NOT NULL,
FOREIGN KEY (Category_Id) REFERENCES Category (Id)
) Engine=InnoDB;
CREATE TABLE Post (
Id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
Post_Name VARCHAR(255) NOT NULL,
Category_Id INT UNSIGNED NOT NULL,
FOREIGN KEY (Category_Id) REFERENCES Category (Id)
) Engine=InnoDB;
CREATE TABLE Post_Fields (
Id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
Post_Id INT UNSIGNED NOT NULL,
Category_Template_Id INT UNSIGNED NOT NULL,
Value VARCHAR(255) NOT NULL,
FOREIGN KEY (Category_Template_Id) REFERENCES Category_Template (Id)
) Engine=InnoDB;
举个例子,假设有属于旅游范畴帖子:
INSERT INTO Category
(Id, Name)
VALUES
(1, 'Where to go?')
;
INSERT INTO Category_Template
(Category_Template_Id, Name, Category_Id)
VALUES
(1, 'Budget', 1),
(2, 'Location', 1),
(3, 'Time', 1)
;
INSERT INTO Post
(PostId, Post_Name, Category_Id)
VALUES
(1, 'America is good', 1),
(2, 'Hot Travel', 1)
;
INSERT INTO Post_Fields
(Id, Post_Id, Category_Template_Id, Value)
VALUES
(1, 1, 1, '1000 $'),
(1, 1, 2, 'New York'),
(1, 1, 3, 'January 2012'),
(1, 2, 1, '2000 $'),
(1, 2, 2, 'Brasil'),
(1, 2, 3, 'May 2012')
;
我想运行一个SQL查询,这将列出所有属于给定类别的帖子,并将这些帖子的所有字段列为单独的列,并将类别模板名称列为列名称。结果应该是这样的:
Post Id Post_Name Budget Location Time 1 America is good 1000 $ New York January 2012 2 Hot Travel 2000 $ Brasil May 2012
我的问题是不同类别的类别模板具有不同的名称,使得它很难写一个通用的查询。例如,旅行类别可以有3个模板(位置,预算,时间),而书籍类别有4个模板(抽象,内容,author_bio,摘要)。当输出列的确切数量会变化时,如何编写一个将一列转换为多列(基于同一行中但另一列中的值)的语句?同样,考虑到输出列的数量会有所不同,我该如何编写一个将一列转换为多列标题的语句?
http://stackoverflow.com/questions/649802/how-to-pivot-a-mysql-entity-attribute-value-schema就是一个例子。您正在寻找PIVOT行到列 – dash 2011-12-25 21:40:55
适当的[示例代码](http://sscce.org/)(这里是SQL语句)比任何ad hoc模式和示例数据格式更有用。请使用'CREATE TABLE'和'INSERT ... VALUES'作为样本。期望的结果不需要作为示例代码呈现。 – outis 2011-12-25 22:48:08
我编辑的问题 – gandil 2011-12-26 13:58:59