mySQL query to get only display - php

Question

I wanted to ask one question as my query skills are not that great and I have been learning mySQL for the last week. This attachment I have shows what happens when I run the following query:
SELECT * FROM clothing, sizing WHERE id = "101";
You might notice that it produces the same id number, same name, same type, same brand_id,same price, and a lot of null values. Is there a query which I can run which only displays columns which do not have null values?

Answer 1

You can select the rows that dont have null values in given columns, or you can use IFNULL.
IFNULL(yourColumn,0)
This will display 0 instead of Null, but beware that NULL and 0 is not the same thing.
Null is "nothing" / undefined, 0 is a numerical value.
You can have issues multiplying with NULL, so you can do for instance:
SELECT (numProducts * IFNULL(productPrice,0))
FROM ...
You can also use CASE or IF to select differenct colums and alias them :-)
External link to docs: https://dev.mysql.com/doc/refman/4.1/en/control-flow-functions.html

Answer 2

Yes above solutions will work only if that column has default value set to null,if its not set then you need to check blank ,i mean to say IFNULL(productPrice,0) will not work you need to do as below,
SELECT (numProducts * IF(productPrice='',0,productPrice))
FROM ...

Answer 3

You are basically asking about two problems that I will address separately in this answer.
1 - More than one record is returned
You should follow mathielo and Olavxxx's comments regarding the use of JOIN.
The query as shown in your question is a cartesian product between your tables clothing and sizing. What the query is basically asking is "I want only the record with id 101 in one of the table, as well as all the records in the other table".
Judging by the rest of your question, this is not what you want. So I take it there is a relationship between rows in clothing and sizing. I will assume that a clothing can only have one size, and that this relationship is represented by a foreign key to sizing. Here the minimum the tables should contain for that to work (I do not reuse your model because from the details in the question I can only guess, not know, what your exact table model is):
clothing:
id: primary key
size_id: foreign key to sizing
sizing:
size_id: primary key
As a consequence, the following query should return all records corresponding to the selected clothing and associated size:
SELECT *
FROM clothing AS c
JOIN sizing AS s ON c.size_id = s.size_id
WHERE c.id = 101
Your relationship between your two tables may actually be different from what I have just modeled. If that is the case, I still hope the above example is enough to get you started in the right direction.
2 - Lots of NULL values
This part of the question needs to be precised. Is it that you do not want the records with NULL values for some columns to be returned, or is it that you just do not want to get the content of these columns? Or maybe you want to use a default value?
If it is the records you want to filter out, you should add <column> IS NOT NULL conditions in your WHERE clause. One for each of the columns you are interested in.
If it is the columns you do not want to get, do not use SELECT * but instead explicitely list the columns you want, for example:
SELECT id, name, price FROM clothing
If it is about using a default value instead, you need to use IF in the SELECT clause as in Supriya's answer. Another example:
SELECT name, size, IF(shoulder IS NULL, 'Default', shoulder)
FROM clothing