从mysql表中列出数据

Question

recipe_category

cid | category
 1  | desserts
 2  | cakes
 3  | biscuits

recipe_name

id | recipe_name       | cid | iid
 1 | black forest cake | 1,2 | 1,2,3,4
 2 | angel cake        | 2   | 1,2,4
 3 | melting moments   | 3   | 2,5
 4 | croquembouche     | 1,3 | 1,5

配料

iid | ingredient_name
 1  | self-raising flour
 2  | milk
 3  | chocolate
 4  | baking powder
 5  | plain flour

我能够使用cid拉取某些食谱来查询数据库,即.甜点:

SELECT * FROM recipe_name WHERE cid='1'

但是,我如何创建一个列表,如下面的成分列出<br>？

黑森林蛋糕:
自发面粉
牛奶
巧克力
发酵粉

我是新手,所以请原谅任何愚蠢的问题!

Answer 1

在单个逗号分隔字段中存储多值属性几乎总是一个坏主意.它使一切都很难查询.

相反,您可能需要考虑使用两个新的交集表来重构您的模式.

这两个表保持原样(只是更改了recipe_categoryto的名称,categories以便不与交集表冲突):

CREATE TABLE categories (
   cid int NOT NULL PRIMARY KEY,
   category_name varchar(50)
) ENGINE=INNODB;

CREATE TABLE ingredients (
   iid int NOT NULL PRIMARY KEY,
   ingredient_name varchar(50)
) ENGINE=INNODB;

recipe_name按如下所示修改表,删除cid和iid字段:

CREATE TABLE recipe_name (
    id int NOT NULL PRIMARY KEY,
    recipe_name varchar(50)
) ENGINE=INNODB;

然后,您可以使用以下两个交集表定义多值关系:

CREATE TABLE recipe_ingredients (
    recipe_id int NOT NULL,
    ingredient_id int NOT NULL,
    PRIMARY KEY (recipe_id, ingredient_id),
    FOREIGN KEY (recipe_id) REFERENCES recipe_name (id),
    FOREIGN KEY (ingredient_id) REFERENCES ingredients (iid)
) ENGINE=INNODB;

CREATE TABLE recipe_categories (
    recipe_id int NOT NULL,
    category_id int NOT NULL,
    PRIMARY KEY (recipe_id, category_id),
    FOREIGN KEY (recipe_id) REFERENCES recipe_name (id),
    FOREIGN KEY (category_id) REFERENCES categories (cid)
) ENGINE=INNODB;

现在让我们用您的示例数据填充这些表:

INSERT INTO categories VALUES (1, 'desserts');
INSERT INTO categories VALUES (2, 'cakes');
INSERT INTO categories VALUES (3, 'biscuits');

INSERT INTO ingredients VALUES(1, 'self-raising flour');
INSERT INTO ingredients VALUES(2, 'milk');
INSERT INTO ingredients VALUES(3, 'chocolate');
INSERT INTO ingredients VALUES(4, 'baking powder');
INSERT INTO ingredients VALUES(5, 'plain flour');

INSERT INTO recipe_name VALUES(1, 'black forest cake');
INSERT INTO recipe_name VALUES(2, 'angel cake');
INSERT INTO recipe_name VALUES(3, 'melting moments');
INSERT INTO recipe_name VALUES(4, 'croquembouche'); 

要定义配方及其成分和类别之间的关系,您需要按如下方式填充交集表:

INSERT INTO recipe_categories VALUES (1, 1);
INSERT INTO recipe_categories VALUES (1, 2);
INSERT INTO recipe_categories VALUES (2, 2);
INSERT INTO recipe_categories VALUES (3, 3);
INSERT INTO recipe_categories VALUES (4, 1);
INSERT INTO recipe_categories VALUES (4, 3);

INSERT INTO recipe_ingredients VALUES (1, 1);
INSERT INTO recipe_ingredients VALUES (1, 2);
INSERT INTO recipe_ingredients VALUES (1, 3);
INSERT INTO recipe_ingredients VALUES (1, 4);
INSERT INTO recipe_ingredients VALUES (2, 1);
INSERT INTO recipe_ingredients VALUES (2, 2);
INSERT INTO recipe_ingredients VALUES (2, 3);
INSERT INTO recipe_ingredients VALUES (3, 2);
INSERT INTO recipe_ingredients VALUES (3, 5);
INSERT INTO recipe_ingredients VALUES (4, 1);
INSERT INTO recipe_ingredients VALUES (4, 5);

最后,构建查询将非常简单:

SELECT i.ingredient_name
FROM   recipe_ingredients ri
JOIN   ingredients i ON (i.iid = ri.ingredient_id)
WHERE  ri.recipe_id = (SELECT id 
                       FROM   recipe_name 
                       WHERE  recipe_name = 'Black Forest Cake');

结果:

+--------------------+
| ingredient_name    |
+--------------------+
| self-raising flour |
| milk               |
| chocolate          |
| baking powder      |
+--------------------+
4 rows in set (0.00 sec)

然后,您可能希望<br>在应用程序代码中而不是在SQL中格式化该结果集(添加s).

但是,如果你真的希望在SQL中这样做,那么MySQL支持方便的GROUP_CONCAT()功能,可以使用如下:

SELECT GROUP_CONCAT(i.ingredient_name separator '<BR>') output
FROM   recipe_ingredients ri
JOIN   ingredients i ON (i.iid = ri.ingredient_id)
WHERE  ri.recipe_id = (SELECT id 
                       FROM   recipe_name 
                       WHERE  recipe_name = 'Black Forest Cake');

结果:

+----------------------------------------------------------+
| output                                                   |
+----------------------------------------------------------+
| self-raising flour<BR>milk<BR>chocolate<BR>baking powder |
+----------------------------------------------------------+
1 row in set (0.00 sec)

转储到HTML中,你很高兴!