I have a bunch of products, and a bunch of category pages. One product can be in multiple categories. So in my database I have a products table with a "categories" column. In this column I store the ID's of all the categories that the current product is stored in, its a string seperated with semicolons.
Example: 1;5;23;35;49;.
When I browse to Category Page ID 5, I want to see all products that have 5; in its categories-column. I currently do this by
SELECT * FROM products WHERE categories LIKE "%".category.";%"
The problem is that this matches more than just 5. It matches 15; or 25; aswell.
So questions:
How do I make sure that I only select the number I want? If category is "5" I do not want it to match 15, 25, 35 and so on.
Maybe this is a very bad way of storing the category-ids. Do you have any suggestions of a different way of storing what products that belong to what category?
Others have mentioned that a junction table is the right way to design the database. SQL has a very nice data structure for storing lists. It is not called a "string", it is called a "table".
But, sometimes one is stuck with data in this format and needs to work with it. In that case, the key is to put the delimiters on both side to prevent the problem you are having:
SELECT *
FROM products
WHERE concat(';', categories) LIKE "%;".category.";%"
Your list already ends in a semicolon, so that is not necessary.
Another more typical MySQL solution is find_in_set():
SELECT *
FROM products
WHERE find_in_set(category, replace(categories, ';', ',') > 0;
It is designed for comma-delimited lists. Odd that MySQL supports such a function when storing lists this way is generally a bad idea, but it does. Still, a junction table is better for performance reasons (and for other reasons).
Answers/comments to your two questions:
The only way I can think of that you could do this without modifying your schema (see #2) is to use a MySQL regular expression but this is really not a good idea. See http://dev.mysql.com/doc/refman/5.1/en/regexp.html for documentation though
You are right - this is not a good way to store categories. What you want is a join also known as a junction table (see http://en.wikipedia.org/wiki/Junction_table). One way would be to have three tables: product, category, and a product_categories table. Product and category would have a unique ID as you already have and the product_categories table would have two columns: product_id and category_id. If product 1 belongs to categories 10 and 11, you would have two rows in the product_categories table: 1,10 and 1,11.
I can elaborate if you need more help but this should get you started in re-architecting your database (more) correctly.
You can try changing your like criteria to "%;".category.";%"
Related
I'm working on something that shows shops under a specific category, however I have an issue because I store the categories of a shop like this in a record with the id of a category. "1,5,12". Now, the problem is if I want to show shops with category 2, it "mistakens" 12 as category 2. This is the SQL right now.
SELECT * FROM shops WHERE shop_cats LIKE '%".$sqlid."%' LIMIT 8
Is there a way to split the record "shop_cats" by a comma in SQL, so it checks the full number? The only way I can think of is to get all the shops, and do it with PHP, but I don't like that as it will take too many resources.
This is a really, really bad way to store categories, for many reasons:
You are storing numbers as strings.
You cannot declare proper foreign key relationships.
A (normal) column in a table should have only one value.
SQL has poor string functions.
The resulting queries cannot take advantage of indexes.
The proper way to store this information in a database is using a junction table, with one row per shop and per category.
Sometimes, we are stuck with other people's really bad design decisions. If this is your case, then you can use FIND_IN_SET():
WHERE FIND_IN_SET($sqlid, shop_cats) > 0
But you should really fix the data structure.
If you can, the correct solution should be to normalize the table, i.e. have a separate row per category, not with commas.
If you can't, this should do the work:
SELECT * FROM shops WHERE CONCAT(',' , shop_cats , ',') LIKE '%,".$sqlid.",%' LIMIT 8
The table shops does not follow 1NF (1st Normal Form) i.e; every column should exactly one value. To avoid that you need to create another table called pivot table which relates two tables (or entities). But to answer your question, the below SQL query should do the trick.
SELECT * FROM shops WHERE concat(',',shop_cats,',') LIKE '%,".$sqlid.",%' LIMIT 8
Does there is a cleaner way to do this ?
The Products table is linked to the sub_categories table, but if there is no sub_categories for a category, I make a link between the Products table and table categories ?
There are a number of ways to achieve this. Depending on the depth level of categories and also what your preferred implementation can implement using either of the following approaches.
Adjacency List model
A single categories table with a self referencing parent_id column that is populated for each sub category.
Nested Set model
A single categories table with "lft" and "rgt" columns to denote the position within the set. "lft" and "rgt" mean Left and Right respectively as "LEFT" and "RIGHT" are reserved words in SQL.
There is a fantastic full blog post with examples and diagrams explaining in great detail how both these approaches work - here.
I would also recommend looking at libraries, in your chosen language, that may take some of the work out what you want to achieve.
Suppose I want to find an article in a database table that includes the text "There were many bison" With phpMyAdmin, I can navigate to Search, choose a field, then choose Like %...%, and it will select the article that includes those words.
I'd like to know if there's a way to find all rows that do NOT include that string.
Let me explain my bigger goal. I'm working on articles about many animal species that are divided into sections on Classification, Distribution, Ecology, etc. Each section can be thought of as an independent article, and I was tempted to make unique tables for each of these sections. However, that would be a logistical nightmare; I'd need literally hundreds of tables.
So I just write one long article with each section beginning with something like this:
So if I have articles about 600 species in my database table, and I want to know which articles DO NOT include an Ecology section, I can simply search for all the rows that do not have that particular div, or something similar (e.g [h2]Ecology[/h2] - though with real tags, not brackets).
Is there a way to do that with phpMyAdmin, MySQL Workbench (which I downloaded and installed just today) or some other tool?
Thanks.
you could use a NOT REGEX http://dev.mysql.com/doc/refman/5.1/en/regexp.html with SQL.
one solution would be to create a categories table on your database and then assign each article a category. That way you could create a query to select all the articles that have the specific category that you want.
example would be :
table articles:
-article_id (primary Key)
-article
-category_cat_id (foreign Key that references cat_id)
table category
- cat_id (primary Key)
-cat_name
a query to select all the articles with the categry of lets say ecology:
SELECT * FROM articles
LEFT JOIN category
ON articles.category_cat_id = category.cat_id
WHERE cat_name != 'ecology'(if you want to select all the articles except those with a ecology cateogry)
another alternative is
WHERE cat_name = 'ecology'( if you want to select all posts with the category of ecology)
Thank you in advance for any help you may be able to offer!
I'm working with an a bit of an odd database where products are related via tags and are not hierarchical.
I'm trying to select a single product using a SKU number from a table and join it with a table of product reviews like so:
SELECT ims.master_sku, ims.title, ims.price,
ims.description, ir.mvp_number, ir.title,
ir.review, ir.rating, ir.created_on
FROM default_inventory_master_skus AS ims
JOIN default_inventory_reviews AS ir
WHERE ims.master_sku = '22284319'
GROUP BY ir.review;
This gives me around 150 rows - which are all the same product but contain different reviews. My question is how can I return just the one product (as a single row) and somehow convert the reviews into columns associated with that one product?
Again - thank you for your time and help.
Rich
You can do that, although it's not "relational".
Looks like someone wants this data in Excel ;).
With MySQL, you will need to generate an SQL statement and execute it. Either within MySQL (in a procedure) or outside (e.g., in PHP). Query first for the pivot column names, put together the statement, then execute it.
An idea of the implementation is here:
http://www.artfulsoftware.com/infotree/queries.php#78
Summary: What is the most efficient way to store information similar to the like system on FB. Aka, a tally of likes is kept, the person who like it is kept etc.
It needs to be associated with a user id so as to know who liked it. The issue is, do you have a column that has a comma delimited list of the id of things that were liked, or do you have a separate column for each like (way too many columns). The info that's stored would be a boolean value (1/0) but needs to be associated with the user as well as the "page" that was liked.
My thought was this:
Column name = likes eg.:
1,2,3,4,5
Aka, the user has "like" the pages that have an id of 1, 2, 3, 4 and 5. To calculate total "likes" a tally would need to be taken and then stored in a database associated with the pages themselves (table already exists).
That seems the best way to me but is there a better option that anyone can think of?
P.S. I'm not doing FB likes but it's the easiest explanation.
EDIT: Similar idea to the plus/neg here on stackoverflow.
In this case the best way would be to create a new table to keep track of the likes. So supposing you have table posts, which has a column post_id which contains all the posts (on which the users can vote). And you have another table users with a column user_id, which contains all the users.
You should create a table likes which has at least two columns, something like like_postid and like_userid. Now, everytime a user likes a post create a new row in this table with the id of the post (the value of post_id from posts) that is liked and the id of the user (the value of user_id from users) that likes the post. Of course you can enter some more columns in the likes table (for instance to keep track of when a like is created).
What you have here is called a many-to-many relationship. Google it to get some more information about it and to find some more advice on how to implement them correctly (you will find that a comma seperated lists of id's will not be one of the best practices).
Update based on comments:
If I'm correct; you want to get a list of all users (ordered by name) who have voted on an artist. You should do that something like:
SELECT Artists.Name, User.Name
FROM Artists
JOIN Votes
ON Votes.page_ID = Artists.ID
JOIN Users
ON Votes.Votes_Userid = Users.User_ID
WHERE Artists.Name = "dfgdfg"
ORDER BY Users.Users_Name
There a strange thing here; the column in your Votes table which contains the artist id seems to be called page_ID. Also you're a bit inconsistent in column names (not really bad, but something to keep in mind if you want to be able to understand your code after leaving it alone for 6 months). In your comment you say that you only make one join, but you actually do two joins. If you specify two table names (like you do: JOIN Users, Votes SQL actually joins these two tables.
Based on the query you posted in the comments I can tell you haven't got much experience using joins. I suggest you read up on how to use them, it will really improve your ability to write good code.