Is there any advantage/disadvantage of storing field value as a JSON array rather than creating new table and one-to-many relationship bet them?

问题

Suppose each user has some numbers(IDs of props in a web game, e.g.) to store in a DB.

I saw some implementations storing the numbers as a JSON string (representing an Array structure) in one field of the user's info table. But my intution is creating another table like below

CREATE TABLE user_numbers (
    userid INT,
    user_number,
    FOREIGN KEY (userid) REFERENCES user_info(id) ON DELETE CASCADE
);

as it's the formal way for a one-to-many relationship.

So I'm wondering does the JSON methods has any practical benefits or it's just a personal choice?

回答1:

In my experience that depends pretty much on the data which is stored. Both ways have advantages and disadvantages. If it's a MMORPG webgame then say you have a PC that has a belt. And the PC may put potions in that belt for a quick access during a battle. So we want to save the ids of the potions, that are stored in the character's belt.

The most common request would be "get all potions that the character X has". And that would run pretty fast in both cases.

The benefits of storing these potion-ids as a separate table:

• You are able to search for a specific potion-id and it's very fast. In-game-example: admins have removed some potion from the game and therefore you need to update everyone's belts
• You can get some nice statistics. In-game-example: look for the most used potion among all players
• The database will maintain the data integrity. In-game-example: you will never encounter a situation when you used the potion and the game says "Oops, a potion with that id does not exist"
• It is good for consistency. In-game-example: you took a potion from the belt and put it into the backpack. The game can implement it by calling a transaction with two simple clear SQL statements.
• You can do JOINs. In-game-example: we need to get a list of potions in the belt along with their names, weights, and images which are stored in the separate table.
• You can update a single item, without needing to update the whole belt. In-game-forced-example: you have a million potions in you belt and you drank one.

The benefits of storing as a json:

• If it's a browser game that uses javascript on the client side, then you get the Belt json object with one simple request instead of doing Select-query and then converting to json
• It is much easier to maintain order of items, since json arrays are ordered already. With the table-approach you would need additional column called "order" and update it every time and check if two items do not have the same order etc.
• You can do a bunch of rearrangement in the Belt on the client side, then click "Apply" — boom, with one query you can update the whole belt. Whereas with the table-approach you would need at least two queries for that (DELETE + INSERT)
• besides, popular DBMS have plugins that support json functions in the database

Bottom line: those are not major advantages and not critical problems. All of them are solvable and with a proper design of the application both solutions will work ok. Before deciding how to store the data, ask youself, what are the most common use-cases for these data and chose the solution afterwards.

回答2:

So I'm wondering does the JSON methods has any practical benefits or it's just a personal choice?

Yes, It's your personal choice to store numbers in array string like "['1','2','3']". But personally I will not recommend this way to store data as it might be possible that you need some arithmetic operation on that or you might need to search result based on that data, in such cases you might need to use some functions and indexes on that. So if you store such like string, then you will not able to do something like this.

来源：https://stackoverflow.com/questions/23709966/is-there-any-advantage-disadvantage-of-storing-field-value-as-a-json-array-rathe