mysql数据库设计一张表很多键值行的性能？

Question

Most of the content types and categories of a project I'm working on has many tables related to each content, pages, blog_articles, blog_tags, recipes, recipes_categories, ads, banners, covers, customers etc.

What all this tables have in common and repeated in each table is title, slug, description, only few of them have other fields, like recipes has ingredients|methods|level_of_difficulty and so on.

What I was thinking is to get rid of many tables and narrow it down to only two tables, kind of like wordpress for posts and postmeta.

For example

content_table
-------------
id
parent_id
type
title
slug
body

content_meta
-------------
id
content_id
type
key
value

In the content_meta I was thinking to do something like this

content_meta
----------------------------------------------------------
| id | content_id | type   | key         | value
----------------------------------------------------------
| 1  | 1          | banner | image       | img.jpg
| 2  | 1          | banner | link_to     | google.com
| 3  | 2          | recipe | ingredient  | milk
| 4  | 2          | recipe | method      | stir it 
| 5  | 2          | recipe | difficulty  | medium

I'm very well aware that for only few types of content the content meta table is going to grow quick

What do you think of this type of design from performance point of view and should I drop it?

Answer 1

It would be a better idea to either merge some tables or remove the redundant columns.

The content_meta idea could make for some pretty nasty queries later on, that concept would likely used when the "key" is dynamic. You'll have to rely on multiple subqueries (or JOINs) for each field in the content_meta table, instead of a single query.

SELECT title, body, ingredient, method FROM content_table 
INNER JOIN recipes ON content_table.content_id = recipes.content_id

VS

SELECT title, body, rIngredient.value 'ingredient', rMethod.value 'method' FROM content_table
LEFT JOIN content_meta rIngredient ON content_table.content_id = rIngredient.content_id AND type = 'recipe' AND key = 'ingredient'
LEFT JOIN content_meta rMethod ON content_table.content_id = rMethod.content_id AND type = 'recipe' AND key = 'method'

You may want to look into database normalization: https://en.wikipedia.org/wiki/Database_normalization