How to make a join in a hierarchical query - sql

Question

I have these two tables:
CREATE TABLE Category
(
curCategory VARCHAR2(50) PRIMARY KEY,
parentCategory VARCHAR(50),
CONSTRAINT check_cat CHECK (curCategory is not null),
CONSTRAINT fk_category1 FOREIGN KEY(parentCategory) REFERENCES Category(curCategory)
);
CREATE TABLE Article
(
name VARCHAR(50)
artCategory VARCHAR(50),
CONSTRAINT pk_article PRIMARY KEY(name),
CONSTRAINT fk_artCategory FOREIGN KEY(artCategory) REFERENCES Category(curCategory)
);
What I want is something like this:
Select
level, curCategory, parentCategory
from
Category
join
article on artCategory = curCategory
start with curCategory = 'Clothes'
connect by prior curCategory = parentCategory
order siblings by curCategory;
I want to print every article which is a clothes. So what I wanted to do is go through every child category including the category itself ('Clothes') and check if the article category matches the curCategory. But when I execute my query I get zero records.

Answer 1

Syntax looks like Oracle so - here's one option which shows what you might do.
Use VARCAHR**2** datatype, not VARCHAR. I shortened columns' length so that the output is easier to display. Also, there was a syntax error (a missing comma at the end of the article.name column declaration).
SQL> create table category (
2 curcategory varchar2(20) primary key,
3 parentcategory varchar2(20),
4 constraint check_cat check ( curcategory is not null ),
5 constraint fk_category1 foreign key ( parentcategory )
6 references category ( curcategory )
7 );
Table created.
SQL> create table article (
2 name varchar2(20),
3 artcategory varchar2(20),
4 constraint pk_article primary key ( name ),
5 constraint fk_artcategory foreign key ( artcategory )
6 references category ( curcategory )
7 );
Table created.
Some sample data:
SQL> select * from category;
CURCATEGORY PARENTCATEGORY
-------------------- --------------------
clothes
trousers clothes
shirts clothes
SQL> select * from article;
NAME ARTCATEGORY
-------------------- --------------------
t-shirt shirts
a-shirt shirts
jeans trousers
SQL>
According to that, the hierarchy should look like this:
clothes
shirts
t-shirt
a-shirt
trousers
jeans
OK, let's make it so.
Out of two tables, using the WITH factoring clause (i.e. a CTE, common table expression), I'm UNION-ing those two tables in order to create a single parent-child source. Then, writing a hierarchical query is a simple matter.
SQL> with source as
2 (select c.parentcategory parent, c.curcategory child
3 from category c
4 union
5 select a.artcategory parent, a.name child
6 from article a
7 )
8 select lpad(' ', 2 * level - 1) || child clothes
9 from source
10 start with parent is null
11 connect by prior child = parent
12 order siblings by child;
CLOTHES
------------------------------------------------------------
clothes
shirts
a-shirt
t-shirt
trousers
jeans
6 rows selected.
SQL>