MySQL查询性能 [英] MySQL query performance

问题描述

我具有以下表格结构:

EVENT_ID(INT)    EVENT_NAME(VARCHAR)    EVENT_DATE(DATETIME)    EVENT_OWNER(INT)

我需要添加字段EVENT_COMMENTS，该字段应该是文本字段或很大的VARCHAR.

I need to add the field EVENT_COMMENTS which should be a text field or a very big VARCHAR.

我在2个地方查询此表，其中一个位于列出所有事件的页面上(在该页面中，我不需要显示event_comments字段).

I have 2 places where I query this table, one is on a page that lists all the events (in that page I do not need to display the event_comments field).

另一个页面将加载特定事件的所有详细信息，我将需要在该页面上显示event_comments字段.

And another page that loads all the details for a specific events, which I will need to display the event_comments field on.

我是否应该使用该事件的event_id和event_comments创建一个额外的表?还是我应该在当前表格中添加该字段?

Should I create an extra table with the event_id and the event_comments for that event? Or should I just add that field on the current table?

换句话说，我要问的是，如果我的表中有一个文本字段，但是我没有SELECT，它会影响对我的表的查询性能吗?/strong>

In other words, what I'm asking is, if I have a text field in my table, but I don't SELECT it, will it affect the performance of the queries to my table?

推荐答案

向表中添加字段会使字段变大.

Adding a field to your table makes it larger.

这意味着:

• 表扫描将花费更多时间
• 较少的记录将适合页面，因此适合高速缓存，因此增加了高速缓存未命中的风险

但是，通过联接选择此字段将花费更多时间.

Selecting this field with a join, however, would take more time.

因此，将此字段添加到此表中会使未选择该字段的查询运行速度较慢，而选择该字段的查询运行速度更快.

So adding this field into this table will make the queries which don't select it run slower, and those which do select it run faster.

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