mysql - どのmysqlメソッドが高速ですか？

Question

私はデータベースに1000文字と言うテキストを保存しています。ただし、最初の200文字しか表示しません。

方法1
最初の200文字を1つの列に保存し、残りをSQLテーブルの2番目の列に保存できます

方法2
すべてを1つの列に保存でき、表示中に200文字を照会できます

Answer 1

It would be "cleaner" to store everything in 1 column. and you can select only the first 200 characters like this

select substring(your_column, 1, 200) as your_column from your_table

Answer 2

It really is irrelevant, but if you try to optimize, then method 1 is better, as long as you limit your query to that column (or you only query these columns you really need), because doing any substring on server side takes time and resources (times number of requests...). Method 2 is cleaner, but you are optimize for time so method 1.

Answer 3

This will come down to one of two things:

If you are pulling the entire row back into PHP and then only showing the first 200 chars, then your network speed will potentially be a bottleneck on the pulling data back:

If on the other hand you have two columns, you will potentially have a bottleneck at your drive access which fetches the data back to your PHP - longer rows can cause a slower access to multiple rows.

This will come down to a server-specific weigh-up. It will really depend on how your server performs. I would suggest running some scenarios where your code tries to pull back a few hundred thousand of each to see how long it takes.

Answer 4

Method 2.

First, duplicate storage of data is usually bad (demoralization). This is certainly true in this case.

Second, it would take longer to write to two tables than one.

Third, you have now made updates and deleted vulnerable to annoying inconsistencies (see #1).

Fourth, unless you are searching the first 200 characters for text, getting data out will be the same for both methods (just select a sub string of the first 200 characters).

Fifth, even if you are searching the first 200 characters, you can index on those, and retrieval speed should be identical.

Sixth, you don't want a database design that limits your UX--what if you need to change to 500 characters? You'll have a lot of work to do.

This is a very obvious case of what not to do in database design.

reference: as answered by Joe Emison http://www.quora.com/MySQL/Which-mysql-method-is-fast