SQL query to get record from tables - mysql

Question

I have a small query to be answered.
There are 4 tables call it as
user : uid, uname
category: cid,canme
product : pid, pname
assemble : aid, uid,pid,cid;
I want to display a record from product table but the requirement is pid(from product) and uid (from user) should not be present in assemble table in the same row at a time.

Answer 1

I believe this is what you're looking for:
select * from user u, product p, assemble a where p.pid not in
(Select pid from assemble) and u.uid not in (select uid from assemble)

Answer 2

Check out this SQL Fiddle and the comments within. You're covering a lot of concepts here, and you'll want to think about your design and what you're trying to accomplish, but to address the goals you've set forth in your question:
You can use PRIMARY KEYS or UNIQUE CONSTRAINTS to ensure that duplicate values don't get inserted into your tables (e.g., you don't want pid and cid to be duplicated in the assemble table, so I made that the primary key). I'm being very literal with your statement:
the requirement is pid(from product) and uid (from user) should not be present in assemble table in the same row at a time. (emphasis mine)
You can use JOINS to relate items from different tables to one another. In fact, your assemble table is often referred to as a "join table". My example is using inner joins (meaning, values must exist in both tables).
You can use FOREIGN KEYS to ensure that columns you want to reference in another table exist there.
Below is the code in case SQL Fiddle misbehaves.
Create and populate the tables:
CREATE TABLE users (
uid serial,
uname text,
CONSTRAINT user_pkey PRIMARY KEY (uid)
);
CREATE TABLE categories (
cid serial,
cname text,
CONSTRAINT cat_pkey PRIMARY KEY (cid)
);
CREATE TABLE products (
pid serial,
pname text,
CONSTRAINT prod_pkey PRIMARY KEY (pid)
);
CREATE TABLE assemble (
join_id serial,
uid bigint,
pid bigint,
cid bigint,
CONSTRAINT assemble_pkey PRIMARY KEY (uid, pid),
CONSTRAINT assemble_user_fkey FOREIGN KEY (uid)
REFERENCES users (uid),
CONSTRAINT assemble_prod_fkey FOREIGN KEY (pid)
REFERENCES products (pid),
CONSTRAINT assemble_cat_fkey FOREIGN KEY (cid)
REFERENCES categories (cid)
);
INSERT INTO users (uname) VALUES ('Akshay');
INSERT INTO users (uname) VALUES ('Mom');
INSERT INTO users (uname) VALUES ('Dad');
INSERT INTO categories (cname) VALUES ('Shoes');
INSERT INTO categories (cname) VALUES ('Hats');
INSERT INTO categories (cname) VALUES ('Coats');
INSERT INTO products (pname) VALUES ('Blue Suede Nikes');
INSERT INTO products (pname) VALUES ('Fedora');
INSERT INTO products (pname) VALUES ('Flying Jacket');
-- Give Akshay a hat
INSERT INTO assemble (uid, cid, pid)
VALUES (
(SELECT uid FROM users WHERE uname='Akshay'),
(SELECT cid FROM categories WHERE cname='Hats'),
(SELECT pid FROM products WHERE pname='Fedora')
);
-- Give Mom a coat
INSERT INTO assemble (uid, cid, pid)
VALUES (
(SELECT uid FROM users WHERE uname='Mom'),
(SELECT cid FROM categories WHERE cname='Coats'),
(SELECT pid FROM products WHERE pname='Flying Jacket')
);
-- Give Dad some shoes
INSERT INTO assemble (uid, cid, pid)
VALUES (
(SELECT uid FROM users WHERE uname='Dad'),
(SELECT cid FROM categories WHERE cname='Shoes'),
(SELECT pid FROM products WHERE pname='Blue Suede Nikes')
);
Queries:
-- get the data out of your assemble table, with names from related tables
SELECT u.uname, c.cname, p.pname
FROM users u
INNER JOIN assemble j
ON u.uid = j.uid
INNER JOIN categories c
ON j.cid = c.cid
INNER JOIN products p
ON p.pid = j.pid;
-- Give Mom the same coat... this will fail due to the PRIMARY KEY, even with a different category
INSERT INTO assemble (uid, cid, pid)
VALUES (
(SELECT uid FROM users WHERE uname='Mom'),
(SELECT cid FROM categories WHERE cname='Hats'),
(SELECT pid FROM products WHERE pname='Flying Jacket')
);