创建Sql子类别表

Question

I have went to give interview today there is question that i didn't hear about, i wana know how to do this ... how to make this with query

create a single table that can hold up till n-level category's. create a table to expandable category tree given the following example . Now the table should be designed in such way that category level can be extended to as much as required .

                                  root
                                  /   \
                                 /     \
                               MEN      women------------
                               / \         /            |
                              /   \       Shirt&top     paints
                         shirt   trousers                /   \ 
                                                        /     \
                                                       /       \
                                                      /         \
                                                    trouser     Skirts and jeans

Answer 1

The "cookbook" solution would be to have a parent id column pointing to a category id in a single table:

CREATE TABLE categories (
    category_id INT PRIMARY KEY,
    parent_id INT REFERENCES category_id,
    name VARCHAR(100)
)

So, for the example given above:

INSERT INTO categories VALUES (1, null, 'root'),
(2, 1, 'Men'),
(3, 2, 'shirt'),
(4, 2, 'trousers'),
(5, 1, 'women'),
(6, 5, 'shirt & top'),
(7, 5, 'pants'),
(8, 7, 'trousers'),
(9, 7, 'skirts and jeans');

Answer 2

If you need to implement that structure in a single table, you could store per row the following information:

1. id (primary key, category id)
2. parent_id (points to the parent category id)
3. category_name (textual representation of the category name)

So in your example, the data would be stored as such:

1 | 0 | root
2 | 1 | MEN
3 | 2 | shirt
4 | 2 | trousers
5 | 1 | women
6 | 5 | shirt & top

... and so on