Question

I have the following table structure:

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

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

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).

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

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?

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?

Answer 1

Adding a field to your table makes it larger.

This means that:

• Table scans will take more time
• Less records will fit into a page and hence into the cache, thus increasing the risk of cache misses

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

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.